Keita is definitely a much much better player than he showed here.
Think the major issue with him was his character. He's shy as hell, not just off the field but on it (with us). That timidness never changed. Five years after he signed he still felt like the new boy. Contrast this with the like of Robbo, big character, who made his presence known in no time.
Those clips of Keita with Leipzig, he looked immense. The way he spun away from danger and accelerated away from an opponent. That 'I'm the boss' type stuff. He does similar with Guinea. We just never saw that here. The game here is quicker and more physical, but that doesn't explain his change in demeanor.
McManaman. He ran the game when he was with us. There were times where a teammate wouldn't even have to pass him the ball, he would take it off his foot and run with it. The confidence was oozing out of him. "Stop McManaman stop Liverpool" the opposition manager's tactic. He goes to Madrid, looks a different player. Making five yard square passes rather than running with the ball, gets rid of it as soon as it came to him when with us it's like he owned it. Completely went into his shell. He had a decent career there (fine goal in a final) but the freedom and joy he had when he played with us was missing. I think Keita is in a similar boat, a player who never replicated the talent he showed when moving from an environment where he was very comfortable to one where he wasn't.