I don't think a lot Gen Z don't like the old.reddit.com because it looks kind of old fashioned vs say react "modern" pages and they're afraid of lookign old-fashioned. However, that is what keeps me coming back along with relative anonymity and content on topics that I like.

information density is too low. Why would I spend 2.5x time scrolling through www.reddit.com/r/fantasyfootball when I can read all the important headlines faster at old.reddit.com ... the redesign also loads fewer posts at a time so you constantly wait for a spinner to fetch new content

Mobile apps solved that problem. The redesign made desktop problems.

I only use my phone when I have to. If I'm within 20 feet of a computer w/ a monitor I'll go use that. I know it's old fashioned but it is what it is.

Do you see yourself ever using a phone docked?

Late Zoomers I think you're correct, however my early Zoomer friends and I all use old reddit - we grew up with it after all.