As i already stated the less ammo is just a valid argument on some guns.
5 guns can be utilized way better by gunners thats true.
We could say 7 guns are ok with a gunner.
But the rest just doesnt get much from a gunner so i rather have another engineer on my ship.
Before you make 2 gunners viable you would have to make 1 gunner viable.
Thats at least for me still a thing. You currently dont need a gunner on many ships.
Lets take the good old metamidion.
You have a gat mortar combination.
The mortars job is to instagib the permahull when the armor is down which he can do even with lesmok rounds. So you dont need a gunner for this gun.
Leaving us with the gatling. It needs heavy clip at longer ranges to hit constantly. This leaves us with a closerange and i mean rly closerange ammo type.
And for me it doesnt matter what ammo type a gunner could add at this point cause i can still use normal rounds as gunner, get a clip of 60 bullets and still do my job getting the armor of the enemy down. I can stay at my gun the whole time, extinguish a fire i may get on it, rebuild it faster as an engineer with my spanner.
Or i could use a buffsetup, still getting and extinguisher in it and still having the same good rebuild/repair as a gunner would have. But with a higher dmg even at longer ranges cause of my buffkit and a decent closerange.
So yes a gunner is useless on certain ships. Just accept it.