Hmm, so they are not very useful? I could see that. Though I do think the long jump is still pretty useful.
Long Jump can have its moments (mainly for when you don't have room to build up running speed to make a bigger jump, the long jump bypasses this need to build up the momentum to a degree) but its jumping arc is lowered raising the chance that you may just end up smacking into the tip of a platforms edge if like me you still hold the properties of the old long jump in mind, some shameful deaths I've had due to this.
The flagpole itself is worth pointing out when it comes to the jumping, a long jump is a reliable way to get the golden flagpole as long as you time it just right so the arc doesn't fall short at the last second, meanwhile it's still possible to use a standard running jump to reach the top of the pole as long as the opportunity to gain some speed is there.
Abilities like those of the Cat and Tanooki suits are big platforming aids, if a stage is designed with verticality then the Cat suit will likely turn up, in turn this means that jumps like the backflip and sideflip that would usually be more handy for these vertical segments end up outclassed by the ability to simply scale the walls as long as you have the suit on hand. Then you've got other character abilities as well as the power ups, Peach, Luigi and
all bring their own boosts to the standard jump, 3D World's jump enhancements come from a different direction to previous 3D Mario games.
There's still the odd circumstance that the other types of jump can come in handy here, spin jump gets the most height if I recall though it's not great for precision. Really it's that the formerly more advanced moves so to speak have their benefits scaled back and the standard jump gets quite a boost as well, you could say these small changes make all the jumps a bit more uniform perhaps for the sake of simplicity and this isn't that much of a bad thing in this game with the more direct obstacle course style it has.
Keeping in mind the other fancier jumps all spawned from Super Mario 64 in the first place which favoured exploration and being a sandbox playground, here in 3D World they're not quite as necessary in standard play and are likely remaining here for traditions sake I guess (though there have been stages like the Shell's Secret in Sunshine that pushes some of those more advanced moves in a traditional platforming format).
I think NSMB games got the blend just right, you never
need the triple jump in that one with standard jumps and powerups being more than enough but you can save time and cut corners using it and the deceptively useful air spin.