Hm? The Affinity Suite already works on Windows, which is realistically Apple's competitor in this space. The only platform moving to the web would enable is Linux and the BSDs, and while that would be great, I don't understand how you think it'd scare Apple?
Affinity Photo is a bit too powerful for the client-side web right now but within the next couple years it's plausible. Photoshop already works in the full-stack browser well. Just a bit of Canva engineering away.