1)
Child Soldiers Prevention Act.
2) Ruined Nami and Ussop's fight
3) Wasted some interesting F6 (Ulti and P1)
4) Undermined Samurai's potential. Implications show that they are not even Gifter-level.
5) Oda sacrificed Scabbard's fights for Tama (Kyoshiro is missing, he could fight Ulti or P1, etc).
6) Triggered BigMom's Child Mode, to save them from Ulti and P1.
7) She outshined Nami and Ussop. Even their comments indicate that they are useless in comparison to Tama.
8) Not giving Momo any feats and focusing on Tama (a completely new character).
9) Tama's feats greater than scabbards's feats. The characters that have been worked on and developed since Punk Hazard, just thrown into dust bin. It is like, Tama is here, now you can go and die.
If this is not enough to convince you that Oda made a mistake with Tama then it is up to you.