The thing is, in the show the Federation say the Dominion can build fleets faster than they could destroy them.
So why can't the Feds, Klingons, or Cardassians do the same thing?
I don't know if the show says anything about automated shipyards, though, and that's the problem.
Just looking at Enterprise's construction in "Booby Trap" it looks too much like they needed manual labor to put the Enterprise together.
When you put together the fact that the Jem Hadar don't sleep, don't need to relax, have no diversions--and they are available to work at all hours of the time/day--
--it makes a lot of sense that they could be the ones building the ships a much faster rate and output.
Just a theory I had
to come with, because yeah, Trek dumbed down a lot of stuff, with no explanation.