Sterling ended his career very early to be honest. He had his golden age at Manchester City. Later on he was like average at Chelsea and still not that bad. But signing for Arsenal was a big mistake for him. 
Pep don't sell until all your juice are empty - Sterling was already becoming a liability to the city team before he was sold, we thought we could revive his career but it didn't work.
I understand why you do not like wage caps but a perfect example of why they are necessary is because it creates a bad atmosphere when one player is earning £350,000 per week and another player that plays the same (or more) number games and maybe is player of the season gets just £50,000 per week until a new contract is negotiated. It is unfair.
Wage caps is not entirely bad but if there should be one, it should be done properly, the FA needs to make it mandatory for all clubs to have one- this way every club can compete fairly in the market.
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Sterling had also returned to Chelsea after his Arsenal loan ended but I doubt he will be welcomed back to train with the first team.
He will not be allowed to train with the senior team yet.