If you can aim yourself, and if you have paid attention to where the subsystems are, they can be taken out rather quickly without even having the ship targeted at all.
I'm a lousy shot but exclusively use fixed weapons (mostly rail/pulse combinations) and don't have issues hitting them myself (I target the ship but usually don't select the PP to shoot it because fixed weapons "micro-gimballing" annoys me), but at least it would make hitting subsystems a little harder than selecting the SS and facing the targets general direction whilst holding fire.
I wouldn't regard gimbals as OP in General and personally just don't use them because the crosshairs flying around my eyes irritate me in the rift - don't have any issues with others using them.
However one of the devs stated that gimbals weren't meant to be used as SS sniping weapons during beta, but I'd say that's currently their main use. There isn't much reason to not target the PP when using gimbals if both, hull and SS targeting only require facing the targets general direction. Their SS targeting accuracy should be decreased or SS targeting should be disabled from gimbals/turrets altogether. Not saying that hitting them with fixed is hard, but at least it requires manually aligning the ship with the target.