I'm going to be blunt with you, just because you can use the special effectively in C rank doesn't mean that it doesn't need fixing.
You're not at the level yet to make good takes about the way the game should be balanced. Ultra Stamp is low tier because weapons like the .52 Gal and Splat Charger, which it's supposed to counter, can just shoot the user through the stamp.
It doesn't work at higher levels, and it needs the fix.
Please do not argue game balance for the sake of liking a special weapon.
It can be your favourite, and you can be good at using it; that's perfectly fine, but that doesn't mean it's good. You should want the thing to be better anyway if you like using it, right? Why argue against a buff?