Yeah except changing your user agent to chrome bypasses the load slowdown lol

Did you test this yourself? Rather than just ask your source, I was going to test it myself. However, I cannot get a slow down at all. Everything is loading instantly and ad-free. Perhaps the servers providing my instance of YouTube don’t have the change, I’m not sure, but I have not been able to personally create this. So without a reliable source or evidence, I cannot just take your word for it that changing the user-agent alone fixed the issue.