With Apollo, do you really need armor any more?
You don't design (or commit to battle) a ship which cannot stand up to the fire of its own weapons unless the fire of those weapons is such that no one can stand up to it. For example, I don't imagine that any present-day naval architect could design a ship that would stand up to a direct hit by a high-kiloton range nuclear warhead, yet during the Cold War, it was considered necessary to deploy nuclear warheads at sea. In that instance, you were designing a ship which could hopefully stand up to conventional weapons, but couldn't possibly [survive] the thermonuclear weapons it also carried. Another possible exception to this would be the torpedo-armed destroyer. Although cases of destroyers surviving single -- or even multiple -- [torpedo hits] were not unheard of, they were extremely rare, and there was no way that you could design and build 2.500-3,000-ton ship which could shrug off the impact of a Japanese "Long Lance" torpedo.
For the most part, however, no responsible navy is going to send its personnel out in death traps, especially when the personnel in question have to be highly trained, highly motivated individuals and not cannon fodder swept up by the press gang. These proposed designs are just that: death traps. Yes, in an absolutely desperate situation, a ship might be pressed into action in this role in exactly the same way that a Union commander at the battle of Gettysburg sent a regiment of infantry into the attack knowing that it could not survive because it was essential for him to buy a handful of additional minutes to deploy the rest of his brigade. Under any other circumstances, the Royal Manticoran Navy is not going to take an unarmored ship, with out point defense capability of its own, into the range envelope of anyone's MDMs, whether those MDMs have Apollo controlled missiles, or not. You may willingly trade a freighter for an SD(P), and in the cold calculation of war, that would have to be considered a win. It is not, however, a "win" for which any responsible commander would play unless the alternatives were as stark as the one the Union general cited above faced at Gettysburg. There is a certain degree of faith that a commander -- and a military service -- are supposed to keep with their own personnel. There are times when that faith cannot be kept, because of technical inferiority as the service cannot overcome, or because of existing logistic or strategic constraints that cannot be avoided. In the long term, however, if you expect people to be willing to die, or risk dying, under your orders, then you must discharge that responsibility to the buy -- as Honor has reflected on more than one occasion -- making certain that their deaths are not wasted and that absolutely no more of them died than you could avoid. Sending unarmored ship's into harm's way unless you have absolutely no other choice is not keeping faith with your personnel.