Future ship design
First, I don't intend to answer all of these questions in anything like comprehensive detail for several reasons, including the fact that I'd like there to be some, oh, I don't know surprises in the books. (By the way, I've been looking at some of the other threads, including speculation on how the Mesan Alignment intends to protect its spider-drive ships, and being a little amused by some of the places you're going and I'm not. In regard to which, all I have to say is tum-te-tum-te-tum . )
Having said that, allow me to address these two specific questions, but first an observation.
Your analogy of a dinghy armed with a 16-inch gun isn't really very applicable. A more reasonable analogy might be the 11-inch guns of the Deutschland-class pocket battleships of the 1930s, although I'd argue even there that what the Manties have in mind is considerably more survivable. The 300,000-ton notional ship they're looking at acquires a very large percentage of its total tonnage from additional defensive elements, including a scaled down version of the Keyhole One platform. As you guys will see in A Rising Thunder, Manticore is already investing considerable effort in defensive doctrine and tactics to deal with the threat of MDMs and even Apollo, despite the fact that no one else has that combination of capabilities. The same thing is true where the Mark 16 is concerned, and the architects and the defensive system designers are considering the new threat parameters in the designs they are proposing. In fact, the Nike-design incorporates a lot of those new features and that's one reason the ship is so damn tough and hard to kill. The RMN has never had any desire to build eggshells armed sledgehammers if it could possibly avoid it. As the Admiralty sees it, they had no option but to do that with the Agamemnons, but that's why the BC(P) has never been particularly popular with the RMN. The type had almost rabid proponents and defenders when it first came along because it was one way to get extended-range missile capability into the fleet's hands quickly and because â?? at the time â?? no one else had the range to engage it, which meant it could operate with relative impunity. Even its fiercest partisans, however, always viewed it as essentially a transitional type, which would be retired to secondary duties (the traditional battlecruiser mission of flag-showing on distant stations, commerce protection, etc.) once the other side acquired MDMs. (And as Mike Henke discovered, concerns about the type's vulnerability once the other side did have MDMs turned out to be well-founded.) The production of the dual-drive missile in the Mark 16 accelerated that process, but it was a direction in which the RMN was already pointed on the basis of its institutional experience and its strategic and operational concepts. The Nikes are not simply designed for combat endurance from an ammunition perspective, but from a survivability perspective, and it is firmly envisioned by the Admiralty that once the other side begins to have MDM capability, the Nikes will revert to a traditional battlecruiser role, as well.
At the same time, the Admiralty doesn't anticipate that the SLN is going to begin deploying MDMs tomorrow, or that Solarian fire control and missile warfare capabilities are going to overtake the Star Empire in any particularly short order. The Admiralty does anticipate that the Sollies will acquire roughly comparable capabilities fairly quickly, at least once it becomes willing to admit that it needs them, but the Manties recognize (realistically) that having roughly equivalent capabilities doesn't necessarily equate to producing roughly equivalent outcomes. It was, after all, the difference in the two sides' tactical sophistication which permitted the German panzers on the Eastern Front to outperform the arguably superior T-34 in 1941 and 1942, and there are countless other examples in which the technique and expertise of an experienced opponent has turned a less competent but technologically equivalent foe into mincemeat. The Manties and the Havenites have a lot of experience in the bank, and their architects and tactical analysts are probably even further ahead of the Sollies in terms of figuring out what comes next than their currently deployed hardware is ahead of the Sollies' currently deployed hardware. The Manties are perfectly prepared to continue using transitional types â?? and types which will become highly vulnerable once the other side has MDMs â?? very aggressively and offensively as long as their range advantage allows them to do so without prohibitive casualties, but they are already looking towards the next generation of warships and warship design. Hence the internal studies which are suggesting a 300,000-ton platform as the minimum to perform the light cruiser/destroyer role. In fact, what is probably going to happen is that the destroyer as a type will effectively disappear, with its independently deployable role reverting to the cruiser and its fleet screening role going to the LAC groups. In that respect, the Roland is every bit as much a short-term, transitional type as the BC(P) ever was, and the Admiralty's internal thinking reflects that. They are absolutely great, galaxy-beating ships to have as long as the other side doesn't have ships with comparable weaponry.
In response to your question about the demise of the BC(L), don't expect to see it happen anytime soon. At some point, navies have to strike a balance between survivability and numbers of deployable platforms. Manticore's preference has always been to err on the side of survivability when possible, which is one reason the jeune ecole's "pragmatic" willingness to accept attritional tactics (and the casualties which went with them) was anathema to the historical school. If you look at current Manticoran designs and doctrine, you'll see the merger of the two positions, with the original proponents of the jeune ecole continuing to lead in technological radicalism but with the historical school tempering their enthusiasm and generally knocking the "panacea-merchants" on the head at every opportunity. The BC(L) design will undoubtedly be further refined as defensive systems and doctrine mature and change, but that "step" on the operational (and tonnage) ladder will undoubtedly remain. The tonnage of the BC(L) is higher than the Admiralty would like to see, but it is probably the lowest tonnage range which will permit the balance between numbers and survivability Manticore is looking for. And it should also be pointed out, I suppose, that over the operational lifetime of a warship (particularly assuming that the Manties can revert to more of a peacetime stance), operational costs are going to enormously outweigh construction costs. The reason I make this point is that there is actually very little difference between the operational costs of a Nike and a Saganami-C. Oh, the heavy cruiser has some edge in the "affordability" department, but nowhere near as much of an edge as it has in the construction cost competition. This means that the economic advantages of the smaller, less capable type are nowhere near as pronounced as one might think. Procurement cost does have to be factored in when it comes to contemplating force mixes, of course, however, and that is where the Nike becomes more desirable than, say, a 4,000,000-ton design which would provide even more tonnage for survivability features and, possibly, permit an all-up MDM armament. The thing is that the Admiralty doesn't want an all-up MDM armament specifically because of the way it would drive up platform sizes (and costs) beyond those necessary for the mission in envisioned for the Nikes and their follow-on designs. (See the paragraph below.)
All of which also leads into your second point about the ammunition capacity of the BC(L). Ammo capacity is a part of the BC(L) design philosophy. A significant part, to be sure, but only a part. The BC(L) is intended to dominate in the face of anything below the wall, and with the increase in defensive capabilities and general all-around toughness, it's going to take something with all-up MDM capability and Manticoran-style laser heads to seriously challenge it. The type is intended for long distance, independent deployment, where ammunition resupply can become a problem; it's intended to stack quite large salvos, despite its limited (compared to a pod-layer design, at any rate) number of launchers, so it can get in a heavy initial salvo if it needs to; it already has Keyhole capability, and Keyhole is a major factor in defensibility; and it's designed for possibly running engagements with large numbers of individually smaller and less capable opponents (dealing with a LAC group, for example, or laying down the law to a "navy" of primarily light units which has crossed the line, like some of the Silesian systems were wont to do). The Saganami-C is actually more likely to disappear than the Nike, to be honest, because the Nike has more endurance and more toughness than the Saganami-C. That doesn't mean by any stretch of the imagination that the Saganami-C is going to simply vanish in the next six weeks, or the next six years, or possibly even the next sixteen years, but it means that the type will find itself being relegated more and more to secondary duties as the opposition's offensive capabilities improve.
All of which, of course, is subject to the non-introduction of additional game-changing technology, he observed innocently.