Good to see you are slowly changing your mind. You started with "he's been shit for 2 years" then moved to he has been shit since December 2019 and now finally he has been painful from December 2020 - so the last 9 months.
I said and proved his numbers for 19/20 were elite. Yes, I was concentrating mainly on goals but I can easily run-off a comparison of all of his stats (all of the ones YOU considered very important for Grealish and more) and for good measure compare with, say, Salah, for both 18/19 and 19/20. Unsurprisingly to me (I've done this before) they are very similar ie elite. The drop-off after 18/19 to 19/20 is not really there. So what specifically was it you think he was failing at for 19/20?
I thought the main problem now with Sterling is that he is NOT scoring goals? Despite his poor touch, miscontrols and inability to kick a ball he was very good at it for 3 seasons 17 to 20 but indisputably lesser so since 20/21 which started 12 months ago. Aguero has gone and, Phil aside, no other player in the squad can get anywhere near his levels for 2017-2020.
I said in a previous post fine lines only were between him and 3 goals in 3 recent appearances. Who knows - maybe the floodgates will open soon for him.