If a user is forced to discontinue use of a subreddit where it's allowed and continues to use subreddits where it's not allowed, then of course you're not going to see an uptick in hate speech. You've done nothing to change their mind, however.
I was once banned there 48h after a polite discussion on the economic costs (citing various sources) for "hate speech". I got too many upvotes so it was noticed. Appealing to a mod resulted in him "examining my posts on other subs, and given who you voted for the ban will be permanent".
Actual hate speech is one thing, but far-left mods of major subs are using the banner of hate speech to silence well-informed opposing views.
If you don't like a subreddit's rules, you're free to create a competing subreddit on the same topic but with different rules, and try to attract people to it.
I moderate a medium-sized (200k-ish subscribers) subreddit, though, so I know how unpopular this idea is with some people.
Reddit doesn't care what people think, but it sure seems to care how many people are willing to use the site.
"hate speech communities" still consist of people. Those people can engage in other hobbies without injecting their political views into everything. Similar how vegans and meat-eaters can dine in the same establishment and atheists and christians can be buried on the same cemeteries.
I would even argue that dedicated places for hatespeech lead to exaggerated expression of mostly reasonable people. Think of trump promising the wall. People cheered him on for that. But that doesn't really mean they want a wall. They might be perfectly happy with stricter immigration policy or enforcement of existing immigration laws too. But shouting "build the wall" is a group ritual for them. Virtue signalling works for both sides.
Edit: After skimming the paper I noticed that the authors were also identifying subreddit-specific lingo. I wouldn't expect this to carry over unmodified to other subreddits. You can still denigrate particular groups without using those particular keywords.