I find the idea that banning Trump supporters killed reddit to be pretty far-fetched.
To the extent there is a change in quality, it probably comes from other factors, including having a bigger, broader, and different user base now than in the past (and only a small portion of that change likely came from Trump-related bans).
Parent didn't say Trump supporters. And I completely agree with their observation. Quality went completely off a cliff around that time. I think it just officially entrenched the Reddit orthodoxy and that there is a "right way" to think, and that infected even non-political subreddits. Not all though, I know some subs are much better and open to discussion than in the past.
To the extent there is a change in quality, it probably comes from other factors, including having a bigger, broader, and different user base now than in the past (and only a small portion of that change likely came from Trump-related bans).