alt Hacker Newshardware-decoded HEIC is around 10x slower than JPEG.
software-decoded HEIC is around 100x slower than JPEG.
WebP is something like 20-50% slower than JPEG, so still solidly an order of magnitude faster than best case hardware-accelerated HEIC decoding.
How slow are we talking though? 10x slower than instant and not noticeable for the average use case? Dog slow and everyone will always notice?