It's impossible to discuss fixed v gimballed and whether the balance is skewed without taking proper account of two factors:
1. Gimbals are not, as so often supposed, assisted-aim fixed.
2. Hit point inflation.
What I mean by point 1 is that because gimbals move independently of the ship, their advantages often cannot be replicated, by anyone.
Example: I boost towards my left. Opponent then boosts towards my right. In many ships, the yaw rate of the nose of the ship itself, with or without FA-off, is so vastly inferior to the gimbal mount's yaw rate that it is impossible, irrespective of skill - simply impossible, via maximum motion rates - for a fixed multi to approach the tracking of a gimballed multi.
It would only be possible if Outfitting sold a fourth option: 'aim your own gimbals'. This currently only exists in crude form via turreted multi-pew. But it would be impractical anyway, without four hands/eyes, whilst also controlling the ship.
By point 2 I am of course referring (again) to 1v1 chaff exhaustion via 2.1 hit point inflation.
Different weapons suffer different degrees of imbalance. But taking the most popular example, the multi-cannon, so long as hit points, shot speed and ship speed remain as they are, I think that fixed DPS would need to be about double gimballed DPS to make a serious 1v1 balanced.