Oh I don't (hugely) have an issue with them in late, but in early?
3X DF (one player) can throw out 18 heavy drones/turn
Wing up with 2 players, each with another DF and you have 3 guys in a fleet that can do spd 31,
throw out 30 drones a turn, and keep 60 in the air. (err space)
Not to many fleets built in early era have that kinda PD.
~ That being said once the 70-75 ships start coming out it's not as much of an issue (imo) and not at all once PF's
are available. (Unless of course you're Lyran, but ..)
And (again) I say Kzin, but the Klinks can approximate it (not as good, but close enough) using F5D's
But Lyran, (I'd assume) Hydran, Gorn, Rom, ISC and maybe Fed (dunno) can't really hold that off.