Let's try it. 20 seconds to first start on a M2 mac mini, not amazing. Search takes about 3-5 seconds. Navigate to video another 3-5 seconds. No 4k. No casting. Can't change the playback speed. Can't jump on timeline with 0-9 keys. Doesn't sync to my other devices. Doesn't know about my membership perks, of course.
After a few minutes I would say this is easily the worst way to watch YouTube short of printing the videos out.