Why would a capital ship be transporting soldiers and equipment into a battle? Wouldn't that function be better handled by a dedicated transport?
Still has to be able to defend itself.
That's why you provide an armed escort, because the transport isn't going to be able to do that and carry the load.
Starfleet's equivalent of a destroyer, or as I think they described it in some ancient volume of noncanonical BEST OF TREK, a flying phaser bank would be the appropriate kind of support.