I think the Mochi Mochi No Mi was underutilized, in terms of creative potential.

Katakuri did some cool stuff with the fruit, like using FS to change his body structure and evade Luffy’s attacks, or create fists with mochi from air, but apart from that, we didn’t really see him do any creative things with the fruit, just powerful moves, but the Mochi Mochi No Mi has much more creative potential than Luffy’s fruit(in my opinion)

Mochi, unlike rubber, is malleable, which allows it to be shaped into different objects, so Katakuri could have turned his fingers into claws, using mochi, then hardening it with Haki, and that would have done incredible damage to Luffy, considering his weakness to cutting attacks, or could have created a ‘Drill Mochi’ or a ‘Spear Mochi’ out of his fists, increasing his range with the stretchiness of mochi, and many more, like turning his leg into a blade, then hardening it with Haki. (This is all my headcanon, and it’s been a while I read WCI, so if I made any mistake anywhere, let me know)