See that's just recency bias. Sterling has been poor/inconsistent for a good few months and mahrez even longer. I'm personally of the opinion that sterling's both mentally and physically worn out from the intensity of the past 3 seasons being the most used player in the squad including internationals and needs a few games off. But this idea that he or the wide forwards isn't as good as theirs is just not true. I could've sworn it was sterling and bernardo who helped fire the team to the league and a domestic treble in a season where they were directly competing against this supposedly much better wide players or did that not happen. This was a season without de-bruyne for the most part so you can't even use the excuse they were carried by him like many of sterling's detractors tend to.
It's funny I watched a game where mane was constantly falling to the floor every chance he got and consistently made the wrong decision whenever he got to the final third just like sterling but because he works hard tracking back people seem to forget that. He's a top player but he's increasing becoming one of the most overrated players in the league that his poor performances always seem to get overlooked. Sterling is every bit as good as him and has shown so countless seasons. He outperforms him in almost every metric you can think of the past 3 seasons including goals, assist, chances created and him currently being out of sorts doesn't erase that fact.