Yaya Toure was worldclass at Barca and early on at City.
Also Keita is born in Spain and grew up there, before moving to Italy at 16. His story is more similar to Pogba and other European-African players who completely went through the european football system.
Only problem with Keita is his attitude. If i remember correctly the only reason why he left Barca for Lazio in 2011 is because Barca didn't want him anymore because of his behaviour. And that pattern has continued at Lazio.