He is a striker, he's just not a lone striker, and nor was Aguero at the same age, it was 4 seasons into his City career before he started always playing on his own up front in 14/15.
His problem is that he comes too deep to help out midfield. When there's 2 strikers it's wonderful, but when he's the only one it means he can win the ball but then there's no one to be passed to, he can't get back in position to get on the end of the move.
Mahrez and Sterling always coming short on their wrong sides is what makes it really ineffective, if you remember back in the day Sané, Jesus, Sterling was a great combination because as soon as Gabby dropped deep, those two would just gun it in behind.
The penalties thing is probably a self fulfilling prophecy at the moment. He has so much extra pressure because of his recent record. He should go away, work on his technique and try again in September.