Funnily enough, responding to someone saying "I literally saw multiple processes eating 1GB+ of RAM" with "This website over here did some measurements and says you're wrong" isn't going to come across as well as you think it is.

I've had Chrome open for some number of days and when I check Activity Monitor, the most RAM-expensive process is currently sitting at <500MB, a few others at 100-300MB, and the rest at under 100MB. The "energy impact" of it is at 160-ish. Whereas, again, Firefox was taking up 1GB+ of RAM in multiple processes and the energy impact was more like 260-ish, my battery was dying way faster, I would see CPU usage of double Chrome regularly, and macOS was always saying that Firefox was using a lot of power. The RAM usage is something I've seen on Windows as well, along with issues with the browser just behaving poorly over time. I just don't see these issues on Chrome or (most of) its derivative browsers. (I've used Brave a lot as well)

Guess I'm just objectively wrong though, because Toms Guide disagrees with what I'm seeing.

No, you're objectively wrong because other users aren't seeing what you're seeing. That's the problem with anecdotes.

I've had Firefox 120 running for days and it's not doing what your strange set up is doing.