I think you're right about Discord.

Reddit never faced the same pressure. The API thing pissed off mobile users, but all of the Reddit alternatives, such as Voat, were hyper polarized politically and were not good destinations for most people. They collected the "worst parts of Reddit" rather than providing a place for the majority of users.

The same thing happened to Twitter. Bluesky is very polarized and constantly gets poked fun at because of it, even by left-leaning folks. Threads was a much more neutral and inviting space that doesn't force you to wear a particular set of politics on your sleeves.

Discord has a few (small) alternatives that aren't alienating or off-putting.