The "never learning new techniques" problem goes for the previous series, too. Always bothered me so thanks for pointing it out. Tenshinhan always only uses his Kikoho. Krillin only ever has his Destructo Disc. Lots of Kamehameha spam.
At least the ToP tried to put a new spin on some old stuff like the Disc and stronger Solar Flare. It also actually did introduce a series of new techniques, which hasn't happened in forever.
Goku using Ki to make a shield around him, the minefield technique and the new Destructo Disc attack are all new. Ultra Instinct is a very different form from any other Goku has gotten. Even the Kamehameha against Kefla tried something new with the technique.
I mean if it bothers you no matter what, nothing to do here, but I'm okay with it if it at least makes sense in context. If it's used because of a legitimate reason. The Mafuba in the FT arc made sense to me, too. It wasn't only there for a callback. There were other reasons for it to be used.
Well,to be fair, Krillin did design Kienzan in Z. And against Saibaimen he used different technique than ever before or after. And he acted as a "proxy" for genki dama (funny that first use of genki dama was more creative than any subsequent). Also Kienzan spam only really happened against Freeza, he became irrelevant fighting-wise after that, and before I think he only used it once against Nappa and Vegeta respectively. Tenshinhan's complaint is legit, but he did fade into obscurity in Z in general. And it's not like Goku didn't use Kamehameha in fresh ways in Z, "IT + Kamehameha" combo became so iconic that it become a signature move in few games. Against Freeza I remember him preparing two from under the water and firing while stying hidden. I agree that UI is nice change compared to other forms.
And Mafuba in FT arc… seeing that it had no consequences and even the "I trained hard to perfect Mafuba but I fucked up with the jar and can't even use it now" joke was there in the original DB... it served as nothing more than a callback. It made sense in the context, but I need more than "making sense" in fiction to entertain me.