Well, that's worse because it's a bigger issue. If you look through some of the bugs (there are several) you'll see suggestions of turning off chat to mitigate the issue but this raises even more questions:

1. Why don't users have to do that with Chrome?

2. While it does help, the video-without-chat CPU+GPU usage is still higher than Chrome's CPU+GPU usage for video-with-chat.

If that also applies to Youtube or other services and has been open for 4+ years then... yeah, big problem.