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.