Yes, well, if they're just "opened" and not fully "loaded", then maybe it can get away with 1.2Gb. ~100 fully loaded tabs, which happens quite often with various online docs, take 24Gb RAM last time I checked. So your figure (2gb for 10) looks quite right to me.
Well, it was worse with Chrome, though not by much: the main memory savings come from Multi-Account Containers, which is a really neat feature, but otherwise they seem almost tied.
Just saying 100 tabs = 1.2 GB or 10 tabs = 2 GB doesn't make much sense as it depends on a lot more things than just the count of the tabs.
You'll need to also outline what pages are in those tabs, how much each tab consumes, what extensions you have installed, how your config looks, what your OS is, how much history you have, what is your usage pattern, what experimental flags have you/the system activated and more.
It just depends on so many variables. 10 tabs of CNN is gonna use way more memory than 100 tabs of Hacker News comments, as a basic example. But you have a content script that is injected on every HN page with live feeds of something, now 1 HN tab might use more memory than 10 tabs of CNN.
Really? On my machine it eats 2gb for 10 tabs.