Nical, do you mind checking the performance on the sites listed above and file new issues for anything that seems new or egregious. If there's nothing we can close this.

https://minergie20.ch/minergie-land

This one is fine.

https://www.goodfour.us/ (just above halfway on the page, "Why Four Hours?" animation)

Still pretty bad explosion of the number of tiles during the splashing animation. I filed bug 1594768.

https://buddhapizza.com/en (top of page problematic, try and scroll down and back up to see)

This one's fine although it could be better (janky at the beginning).

https://listedbuildingsurveys.co.uk/ (halfway down page, "Uncovering the past" animation)

Not horrible but still quite a bit worse than non-webrender (less than half the frame rate). Although the time spent seems to be mostly in skia code. It is possible that frame scheduling is playing against us in this case. Also possible that the way we replay a complex stroke on many tiles is slower than doing the same on fewer bigger tiles. Invalidation and layerization looks reasonable.

https://listedbuildingsurveys.co.uk/ (halfway down page, "Uncovering the past" animation)

I filed bug 1594789 about this one. It's a unique situation which we could definitely do better on.