Perhaps you have a few points, but your points are made with the assumption that the fleet will always have the resources available to defend this thing from close attack by strike craft and other nastiness. That just is not sound military thinking, or planning, from a designers perspective.
While long range fire-support is indeed a desirable commodity, I find that I simply cannot argue against Mad Bomber's logic, and not because it goes along with what I said earlier, but because his statements reflect a designer's logic that I find to be concrete. If you want to plead your case for LR Beams, you should try presenting arguements of an alternative logic that is at least believable and truely addresses that arguements currently on the table. So far, your remarks seem to merely treat those arguements of balance and logic as though they simply do not matter or are completely irrevelant.
Does the ship really
have to have a specialized role? No, it does not. Various corporations create weapon systems that are designed to compete with existing systems all the time. You have any idea how many differant companies have tried to convince the US military to replace the M-16A2/M-4A1 with
their new, fancy battle rifle? Tons. The Royal Army has had to put up with the same stuff, as have many others. How many different classes of Frigates, Destroyers, and Cruisers are there in the US and Royal Navies that perform the same mission? Quite a few. For that matter, does not the Aeolus perform the same role as the Leviathan? Yup. Of course the Aeolus is a bad example since so few were produced, but whatever.
As far as the Trebs, I again agree with MB that they would be a bad idea. Although I doubt heat would be an issue (surely modern cooling devices would prevent problems), in the interest of balance I would re-state my suggestion for a smaller, medium range system. In addition to that, Trebs are quite large as far as missiles go. Logic dictates that the designer must consider space for reloads, as well as the mechanics of actually reloading the weapon system. A significant amount of space on a hull that we are cramming

of other stuff into already.
In the end it does not really matter how you choose to table it anyway. I tend to change tables to my own whims and needs so it does not really matter much to me. My only concern at this point is the actual sub-models used for the turrets and how they are placed. In the end it those decisions that open up the true possibilities.