If you look at other low build weapons, they're generally built for early game and lack the strength to be truly viable at end game. The havoc however has both these positives.
Yes it has a spool up time...we all know this, and that literally makes no difference due to its high firerate/damage per shot more than making up for this disadvantage.
It either needs the spool up removing and base damage reducing or mag capacity dropping. It really is too convenient a weapon in its current form.
To make the thing even more annoying it seems to be considerably more frequently spawned than any other AR.