Take paper and pen and count the damage of the same weapo on all hardpoint.
If you'll do that you'll get 121 for cutter and 119 for vette if memory serves me well.
What weapons are you using for that? I can't find any loadout that gives those numbers.
Going with full fixed pulses has the Corvette leading by 111.9 to 111.5, with gimballed at 89.9 for the Corvette and 89.6 for the Cutter. With bursts, the Vette leads 127.8 to 126.2 for fixed and 101.8 to 100.0 for gimballed. Same thing with beams, the Corvette gets more DPS. A full laser build on a Vette
will do more damage than a Cutter
Admittedly, The Cutter does get more DPS for multicannons, although as soon as you start shooting at anything thicker than a T-9, the piercing values on the Corvette's huge hardpoints gives it the superior DPS. The Cutter also does slightly better with cannons too (raw DPS is a 2-3 points higher), although you still don't get the numbers that you cited.
I'm not going to count loadouts for full mines, frags, missiles, or torps, since none of these come in huge hardpoints and you would need to be missing most of your brain to think that they would be a good idea on a ship that has a main selling point of twin huge hardpoints. Besides that, mines/frags are pretty useless on large ships and torps/missiles have severely limited ammo counts. I would avoid these weapons on a Cutter or Corvette wherever possible.
PAs skew the DPS in favour of the Cutter, but that is because there are no small PAs. If we remove 2 of the PAs from the Cutter to even out the loadout, the Corvette pulls ahead. If we add railguns to the 2 remaining slots on each ship, the Cutter is back in the lead (although good luck landing railgun shots in a Cutter).
None of this takes into account the Corvette's better power distributor, or the fact that the Corvette does not need to rely on turrets and gimbals to do damage. While in certain situations the Cutter
appears to have superior firepower, it will struggle to fully utilize it in situations where as the Vette will have far fewer problems.
Just because I'm curious, where did you get the 121 and 119 figures from? What weapon types were you using, and were they fixed or gimballed?