Wouldn't deprioritizing interfere with regular web traffic these days, given that close to one third of non-bot traffic reported by Cloudflare is over UDP with HTTP/3[0]?

[0]: https://radar.cloudflare.com/adoption-and-usage?dateRange=52...

I'd certainly hope ISP follow your reasoning. BTW that was why I put my WireGuard server on port 443, hoping it would avoid the tragic QoS…