I think most people would agree that there was no reason for Axel to get a Keyblade as he was fine just the way he was. It was fanservice, I know it, those who play KH know it, even Nomura knows it, he just doesn't want to admit it.
I rather not get into his inept head though, because the excuse he gave for it was blatant crap since...well, it was bs even without this, but Lea was ultimately not the one that helped return his friends and the role was instead given to Saïx for a half-assed "redemption" arc.
Naminè technically already has a unique power. And it's not that Nomura doesn't use it well. The girl is absurdly powerful and the characters should thank the Heavens that she wasn't made a villain.
The problem stems from the trios and the incessant, obsessed need to have them. Those not in it, don't get anything. It's a complete detriment to everything and the cast suffers from it as a whole. There's no synergy. KHIII would have been the chance for them to get at least a few sentences in, but they decided to stay uncaring and unresponsive to events while Sora took care of the actual proper reactions and concern for them. It was a joke.
Kairi and Naminè are legit some of the most badly treated female characters I've ever seen. Naminè was doing fine until KHIII happened and all she was worth there was to be a replica's trophy. Yet Nomura proceeds to break a leg and arm for those who inherit the XY chromosome. Saïx, Axel, Diz, fucking Xehanort, Riku Replica, Demyx, Luxord, Marluxia, etc.
Oh, I forgot Strelitzia to add to the Kairi group. Doesn't constitute as a character and merely existed to give Lauriam his Onii-chan manpain. That's a worst fate than the other two.