I think the comparison with Sturridge is a bit bizarre in that Sturridge is now 26, and basically could progress a bit more (if not injured) but is more or less the finished product. Sterling is still very much a work in progress. His breakthrough season was fantastic but probably a bit lucky due to various circumstances (he was an unknown factor, playing in a very attacking team, with 2 strikers in great form around him) so his performance level was probably elevated. The 2 following ones have had other circumstances that, for me, make it impossible to judge him too harshly: in his last season at Liverpool, he was basically the one who was meant to make everything happen (which for me wasn't fair for a kid so young), and the overall team performance was quite poor, and he was clearly unhappy in the second part of the season. This season he hasn't been fantastic, but he's got a huge price tag to live up to, is playing in a position that's not really suited for him (as
@ThierryHenry said), and he's not actually been that bad. Just inconsistent, as you'd probably expect for a player his age.
I don't really have huge sympathy for him (he played for Liverpool and now City), but I think people are unfairly harsh with him and with good guidance, which he could have under Pep, he could turn out to be an excellent player.