You also get a few choices in your setup
exemple : KM 3x11" peashotter vs 14.96" at BB2 level.
USN 12" or 14" at the pre-BB2 remod BB1s (NM30 penn30 tenn41)
On a lesser level mini-monty colo and tenn, or using NC with sodak guns(altough this would be kinda pointless)
UK check the BB3s choice. 3x16", block low ranged quad Ns or long range crap spread quad Ls. Unless it totally changed, Revenge could use the RP12 D back in the day I think too.
IJN you got 2 very viable setup for BB123s (Kongo can use fuso's N, fuso naggy's D and naggy has 2 possible set)
On lower levels:
USN has 3 set of 3x8" for their later CAs, dual 8" or triple 6" for their CL2 (and CL3 if you consider cleveland so). Tons of different guns are availaible to their DDs.
KM, the M pro and kberg can run 3x5.9, 2x6.75 or 2x8 Ds (AH ones). 2 sets of 2x8". Also MANY possibilities for their DDs.
IJN you get 3x6,1 Ns for block, L for range, or again the higher ranged 7,9". 2 sets of 2x8" also.
UK has CAs offering 2 very different playstyle, based on HAW or direct fire. Again gun choice for both DD and CL is kinda overwhelming.
MN lacks that variety. You mainly choose a great gun with crap ammo, or a lesser one with more ammo. But you dont have a "different" setup for them.
(note that I'd like to get a better look at their CA (seem to have a decently ranged HAW option with trips) and in the process of leveling one. But BBs pretty much are 1 BB - 1 gun)