I was going to say something very similar but I wouldn’t put the lack of documentation for “will-change” on mobile all on him. What he’s saying here reflects what a lot of other articles say and none of them touch on the mobile problem.
This is the root issue with “will-change” for me. In order to get it right it needs a way for the user to hint at its need ( ie. with a mouse ). I haven’t personally spent a ton of time thinking about how it would work on mobile (and I really should) but what disheartens me is that it seems like this use case is being near ignored by everyone thinking and talking about it.
In my opinion, without a viable solution to touch screen “will-change” is far from a perfect solution.