I recently switched to Zen with Ublock Origin and it does seem like some sites are slower than before. It's got me suspicious that site owners are increasingly throttling users with adblockers. YouTube absolutely does.

Zen is my favorite browser experience by far, and I've been using the web since Netscape in 1994. But the slowdowns do put a damper on things. Also some of the streaming platforms don't seem to play nice with it.