Valid points for including a few 20mm Oerlikon single mounts… but not complex maintenance-intensive mini-gun-style weapons.

Nope. Not in the same context.

That kind of 20/23mm cannon is part of a ships light gun fit and requires a trained gunner. That kind of mount requires no small amount of skill to get results with. Completely different to the 50cal type weapon thats being discussed here which would be manned by any old stoker who volunteered to have a crack at a new duty.

It doesnt make the blindest bit of difference what the relative destructive power of a cannon shell is over a 50 cal if the guy firing the weapon cant hit the target. As stated the gatling takes the kind of coverage offered by the M2 type weapons already used and magnifies them for very little additional ship impact.

Complex and maintenance intensive is a bit of a stretch. Gatlings have always been more reliable shot-for-shot, with equal maintenance, than any other type of cannon I’m aware of.