That certainly applies to the biggest subs, but there are usually still high-quality subs for most topics.

Small subs are more diverse and accommodating IME. Worse than popular though are flaired-only subs. They are so heavily moderated that posting feels like an exercise in guess-the-unspoken rules.

Because they also ban everyone they disagree with

There isn’t one “they”, each subreddit does its own moderation

There are still networks that ban users for posting on /r/Israel and /r/Jewish. Famously the ones that run /r/interestingasfuck, /r/therewasanattempt, /r/soccer. /r/bannedforbeingjewish tracked this until it was banned.

Reddit itself can and still do ban users at site-level.

Which would be fine if there was a good reason to do so but there often isn't