But if you increase the userbase, you'll end up with more ppl who like yugioh and want a community which leads to duplicate communities. But for niche topics, the duplicate communities are likely to end up with userbases too small to sustain enough activity. A way to combine communities makes it more likely that users find other users who want to discuss niche topics with them. That helps to grow the userbase.

There is no point

Yes, there is. If we can keep those 5 users here, its better than them being on reddit. There's no reason not to work on this. We have multiple projects, each with multiple contributors, so we can do multiple things at one time.