It's because you're really not dealing with the full kit of Ninjutsu. at that level
Fuma is mainly used in TCJ as your first jutsu since the potency increased. In the earlier days you would use it more often since going into Raiton would be clipping a GCD.

Raiton is still used frequently so it's not outshined.

Hyoton is pretty pointless which is why at 76 they upgraded when used under Kassatsu and it's the most damaging jutsu out of the toolkit.

Katon offers the base potency, but pending on how many mobs there are it would make more sense to doton. Don't know math off hand but the server ticks for damage would take over Katon's base damage pretty overtime. Though in most pulls you generally will have two jutsus good to go after using hide so you can just doton then katon. Katon does get upgraded at 76 which does shift the balance so it's something to look forward to.