"I can answer this! According to various sources (mainly, complaints on the redesign subreddit), the new.reddit interface is a lot less tolerant of timeouts and delays. Old.reddit was much more relaxed and would wait longer before throwing up errors (like logouts and such), but new.reddit is RESPONSIVE!, and the backend isn't playing nice with the new, tighter tolerances."
Full AMA https://old.reddit.com/r/sysadmin/comments/9x577m/were_reddi...
Also a 2018 AMA summaryhttps://github.com/yanhan/notes/blob/master/reddit-sysadmins...
Compare Old reddit and New reddit by shrinking your browser window in the x-axis on desktop.
They've also made major efforts to keep the site socially sane for the majority of users (for better or worse, IMO generally better) with their moderation model.
Whether or not it's a great site technically is irrelevant. It's something people want and something I keep coming back to because there's no equivalent when it comes to niche communities.
Niche specific forums are better at everything niche communities want/need in a discussion space except bringing on new users. Considering the kinds of users you get when you're in close proximity to a colossus of internet riff-raff I don't think this is a big tradeoff.