the post clearly implies that opting for independent hosting instead of creating a subreddit (the admittedly easier route, for community building as well as technologically) for a niche forum indicates a "sense of grandeur"
You might be kind of young, so there was this time when "Facebook for health" and "amazon for X" were used as legitimate pitch items as a way to frame the potential of whatever CRUD app someone was selling as a billion dollar visionary idea. It was very tiring. The modern equivalent is something like a "DALL-E 0llamma MLA is all you need" post about a random arvix article about ML
What if such feeling is justified? Everything else equal, I'd rather have a community not belong to Reddit, and I'd be horrified if HN somehow "migrated" to being a sub, the difference between communities is enormous.