I have also noticed this since the latest update (Version 0.99.121-beta), I have attached a screen recording, comparing Safari to Orion when watching the same YouTube video, in the same quality.
That being said, the increase in CPU usage since the most recent update has not only been while watching YouTube videos, I have noticed an increase in battery usage overall, which I assume to be the fault of increased CPU usage whilst browsing generally.
Like I said, I have only noticed this since the latest update and everything prior to that update has been perfect, Orion has been the most battery efficient browser I have ever used.
I'm running MacOS 12.4 on a MacBook Air (M1, 2020), if there is any other information/logs I can provide please let me know.