That super railgun will be good only against big ships, as it'll be too clumsy to aim at anything small and nimble.
Overpenetration is a thing, so even if you manage to hit small ship, the effect will be exactly the same as with current railgun: small hole that goes all the way through.
And will have exactly the same range as current one. Because range is hard capped at 5km (visual range) and soft capped by accuracy and bullet travel time.
Thus big ships and stations will be dying even more easily, small ships won't be affected at all.
I always saw the plasma thrower as the logical "big gun" that deserved an upsizing, but the community as a whole is also extremely affectionate towards the modular-length mega railcannon.
As far as logistics, the carrier promises to take more players off the front line to support carrier ops, the BB and DNs actually have more direct combat roles comparatively. Where the carrier shines is that the fighters don't need to be as spaceworthy as the battleship to travel, a hole in the BB means it suffers under warp forces, the carrier is a "warp classed" platform if it has an enclosed deck. All things being equal tho, a squadron of fighters may have advantage over a single large ship, but the large ship will lose less firepower under attrition compared to the fighters but is more vulnerable to big guns. It's a fun balancing act.
Regarding crew: the whole small vs large is about which approach use manpower the most efficiently.
Single 10 people frigate or carrier+8 fighters. Both require the same amount of people to operate, and roughly the same amount of resources.