If all those things were easier - maybe dirt-cheap turnkey hosting for something federated like Lemmy or whatever - then perhaps the answer to "viable Reddit competitor" is no Reddit at all, but just each subreddit go off and do its own thing. Your stamp-collecting forum doesn't need Reddit scale, it just needs a donate button for a few bucks a month, and if it's connected to the Fediverse then people can use a single login or app to switch between all their forums like they do with subreddits with a single federated timeline/notifications to keep them posted.
You could set up a phpBB forum or something like that almost for free on one of the cheap DIY webhosts like nearlyfreespeech, but you'd need to take the time to install. It would still be pretty easy though.
These things still exist. But people will switch to Discord instead because most subreddits seem to have discords already.
