Nah. AI-generated content doesn't "ruin" the internet any more than Disney can "ruin" Star Wars.
The good stuff is still there. Always has been. Low effort Sora vids don't reduce the entertainment value of - say - Tom Scott's oeuvre.
What AI spam does its the same thing all spam has ever done - increases the amount of noise we have to filter.
Noise is always cheaper to manufacture than signal so it always appears to dominate. ... but any given noise has no lasting commercial value, while high quality signal always does. That's why the old newspaper companies are still around even when you can just read Twitter to get the gist of world events.
Intelligence and thoughtful design matter.
We're gonna see a lot of AI spam for a couple years. But I promise you someone is already working hard to figure out how to identify it.
When I first joined the internet it was considered virtually impossible to detect and block spam reliably. Now, email spam is a rare annoyance that only impacts us occasionally.
Someone will crack AI-detection, or better yet, solve "this is noise" detection once and for all.