That is indeed true. Only issue I can see is the copycat community might not outgrow the older community. And I think people tend to gravitate towards the larger community if there are multiples of them.

Thankfully the Fediverse designates community size by active users per week/month/etc when you look them up. Piefed specifically does this. You can’t even see the overall subscribers in the community browser. So this levels the playing field somewhat.