Imagine with Mazraoui-level full-back, simply standing still, given enough time, becomes threatening, as everyone on the pitch knows he's thundering forward on the over or underlap and all you've to do is hold your position and a world class option arrives. That simple lay off you then make looks like an immaculate part of a chained attack and you are immediately bought the time you need to make a secondary run, literally off the back (contingent) to the primary run of this Mazraoui-level player. Over time, really simple actions will build and you will look impressive and like you have very good decision making.
Take that Mazraoui-level full-back away, and Antony doing the same things looks lost and indecisive, especially when more often than not now, he'll be left having to go 1on1, or making a much tighter pass infield because nobody has provided a decoy run that opens easy passing lanes up. At Ajax, Antony didn't have to play as rushed as he does now and he didn't have to go 1on1; he couldn't be isolated with a full-back for very long because Ajax were the dominant team and spent the majority of their time swarming the opposition. Antony had his niche there and served a really useful purpose. He's got like a third of that use here as things stand.
I think it'll be incredibly difficult for him to unlearn a game he's reaped so much success from and had been executing since he got to Europe (?), I've never seen him in the Brasilero to comment on his game there, but I would not be in the least bit surprised if it followed the same principles, especially with their appreciation of the full-back's contribution to the attack.
Thing is, Antony should have a finite amount of time before others are given a go. I don't think it's right he gets to hog PT and others get hooked for weeks/months for games equally as bad as his. I also think this world class FB thing isn't just to his benefit as we have 3 wide playmakers at the club all of whom are RW's, and guess what? Said player would do wonders for the other two as well, and they are superior talents to Antony at base ends on top of that, so why should he be catered for in lieu of others?