I'd prefer to think Sergio is just in a slump and can get back to the levels he hit before because if it is the style of play, we need to get someone else up top. Lewandowski managed a goal a game against the same parked buses, it's not impossible, you don't need to be Messi score bucket loads of goals in a Pep side outscoring our closest rivals in the league by a goal a game.
If Aguero was ghosting through games, not gettinh into positions and being ineffectual it would be more alarming. Missing chances, when putting effor in and getting into goalscoring positions, is just evidence of a slump to me.