I'm a bit wary of the idea of bolting multiple fully functional starships together. I mean, it makes sense in certain circumstances and is a visually cool concept, but Trek so far has not demonstrated those circumstances and Starfleet has not adopted the technique. It's still considered radical in the 2370s, as of "Message in a Bottle", and doesn't seem to be catching on.
Then again, small, crewed fightercraft were similarly anathema to Star Trek originally, but modern Trek has carved a niche for them as soon as portraying them became technologically and budgetarily possible. And we certainly shouldn't argue "this is not logical, therefore it can't be" when Star Trek actually gives us something as an explicit fact. Rather, we should start rubbing our heads together in an attempt to justify what has been shown to exist.
FWIW, we weren't shown modular "warheads" for the Galaxy
class in DS9, even though that would have been a natural time and place for them to appear. But we could argue we were shown "warheads" on the Nebulas
, with Starfleet moving from a more peaceful stance as with the Phoenix
of "The Wounded" to a more warlike one as with the supposedly recently refitted Sutherland