He is playing for, maybe, the best team in the world. Of course he has plenty of qualities. His movement is world-class, his pace and counterattack ability are also great. But again, all of these qualities are useful if he scores goals. Players like KDB, Foden, Grealish, Silva, Jesus can have great games with 0 goals and 0 assists, Sterling can’t. His abilities are all tied to his numbers. And that’s why no one is gonna criticize other players as much when they don’t score.
A comparison I like is Xavi, Zidane and Iniesta with Lampard. Lampard has 3 times the amount of goals of the others. Not one manager would choose Lampard ahead of the other 3. And Lampard gives much more to his team than only his goals.
To know how relevant the numbers are for a player you need to watch him constantly. That’s why I hate the argument of X scored 20 goals so he had a much better season than Y who only scored 10.