I'm a firm believer we need to be playing 4-5-1. However, with the way Pellegrini sets up his 4-5-1 there's not really any of the benefits you get from an extra midfielder and it's more just a way of shoehorning players into the side. Defensively, we get no extra solidity as we've usually got Silva, KDB and Yaya on the pitch who aren't putting in the defensive display needed. Going forward, you need quick incisive passing combined with clever off the ball movements to get the most out of the formation. We currently are seeing none of that. Pairing kelechi with Aguero seems like a good idea right now if pellegrini isn't going to use 4-5-1 correctly. We'll get no less protection than usual as Kelechi is probably a more willing worker defensively than the likes of Silva or KDB and going forward we've got double the threat upfront, kun gets somebody to work with and the midfielders are less likely to be played out of position. Didn't think i'd find myself saying this but right now i think 4-4-2 would be worth a go in some not all games.
