There's little doubt he's capable of being their main man up front. His stats are way more impressive than Calvin-Lewin's. I haven't seen Calvin-Lewin play, so can't comment on him generally but he's got three years on Kean, about five times more caps but almost the same amount of goals.
It's pretty normal that a young player from a foreign country and league should be weened up the hierarchy. With mature, proven players it's different. The explanation that he hasn't proven he's adapted in training might be entirely true, but I reckon they know how good Kean is going to be and its just a pretence for keeping him grounded and to send a message to the squad about merit and earning your place early in the season.
I think he'll suit the EPL just fine. Would love a good explanation from Paratici though as to why he was sold. Makes such little sense even now. I can only think that Paratici can't cull old duds and Kean was simply a quick, easy and short term (short-sighted) solution to his problem.