Here's what people forget.
The riskiest position in football is DM. How many have come to the PL with great reps and left a shadow of themselves. We've had loads ourselves. Garcia, Fernando come to mind and I'm sure there's more.
So far I've watched Fabinho and Jorginho(I know, pre-season etc) and both have looked shockingly off pace. Now this may be pre-season, but it's pretty commonplace that these players struggle to adapt to the pace/tempo.
He's one of them.
The other thing is people fail to realise that in great teams, average players can look great because everyone occupies the opposition.
Look at Stephen Ireland. Teams were so focused on Robinho and Elano that Ireland looked world class.
I said this of Mhktayrian when he signed for the rags, he was a cog in a machine and made look very good.
I would say Bakayoko was surrounded by special players and as a result he's had more time and space than afforded at Chelsea.