Keita is a decent player and thats it. He has no extraordinary skill what so ever. He isn't that great going forward, with the occasional decent ball and isn't that great at positioning either. He's ok defensively and isn't the best at passing quickly or distributing the ball under pressure. Overall he's a very average player besides that great, short start to the season he had last year. I like Ozil but with our front line he's not breaking into our 4-3-3 or even a 4-3-1-2 given it'd be the same players. He'd start as an attacking midfielder imo and only if Xaviesta isn't in, all three could play but one would have to drop back.... (not the worst idea considering how Iniesta is a glass cannon).
I don't think Keita would be the ideal defensive 3rd member of our midfield, Sergi being the obvious choice. To me it'd just make sense to transfer Keita, bring in Ozil as in an actual different/effective attacking midfielder option and just bring in a strict defensive midfielder. Buy someone who is GREAT at their jobs, not decent at everything. We got enough flexible players between Maxwell and now Adriano, not even counting JDS or Thiago.
For me its either JDS + Thiago or Ozil + defensive mid (transfer Keita) would be best for the team.