I did, too. All I can tell you is that when I have Brave running on an M1 with four tabs open, it's consistently using 240MB of memory. When I fire up Firefox Developer Edition with the same tabs open, it starts at 660MB and quickly balloons up to 1.05GB of memory usage.
My experience also. I’ve slowly edged away from Firefox and have primarily been using Brave and Safari for the last 6mos or so. Brave just feels snappier, and it’s close enough to Chrome that most work required websites aren’t broken.
I currently have a number of Google Docs and Sheets open in Brave. Because of your comment, I started poking around. Try as I might, I couldn't break anything. That probably doesn't mean there's absolutely no way anything could be broken, but just anecdotal—I couldn't find anything.