So strange, yes I can select the greyed-out barbettes, and even though the game tells me 'NO MOUNTS', I can actually place them. I'm 100% sure that this was not the case before.
This makes it just a bit more bearable, but still my argument stands. Most cruiser lines are very boring with samey ships for a loooong time, and (flush-decked is too late in the tree) and then finally all the later hulls get rushed one after the other really fast.