This is not UE marketplace, users on Sketchfab very often upload assets with a single object. This will hurt legitimate creators way more, as instead of making an asset in 3 days, they will have to spend 30 days to make the 10.
As for someone spamming AI content, they would just need to tweak their bot, so instead of it taking a few minutes, it will take like 20 minutes instead.
There might be 10 times less AI garbage, but there also will be 10 times less real content. So the problem stays the same.