Well done article. What'd I'd really like to see though is a comparison at 5X zoom. In reality, anything beyond 5X zoom is going to make up a very tiny fraction of the shots taken. I think a comparison at 5X is more realistic for showing a more common zoom shot. 10X is great for showing the how the better zoom camera starts to really pull away. But I would suspect they are very similar at 2X-5X.
Also, I think one could say it's a bit "unfair" to compare the two considering they were not designed and released around the same time. The fact you are comparing a 20 series to a 21 and it's actually rather close speaks a lot for the Note 20. Really the only complaint I've heard about the 21 Ultra is it's a tad too bulky and heavy even for those used to carrying large phones. The fact the Note is a better weight/size and still packs an S-Pen inside is simply amazing.
I think the 21 series also has a new improved larger fingerprint sensor (sorry if I missed that comment) which is possibly other than the cameras, could be the best improvement for a lot of people tired of the finicky sensor in previous models.
Really, the S21 Ultra is the no brainer if you just want the best cameras available on an Android phone that isn't a Chinese model that is banned from Google Play (whether you really need that quality of cameras or not as the Note's cameras beat about 90% from that year.)
It's like choose (a) best/latest cameras or (b) close second on cameras + SD-Card Slot + Built-In S-Pen. You decide.