Simply by choosing a lesser used fedi software you’re helping keep the fediverse from being dictated by a single software’s whims. So that’s a big plus there. Federation issues with kbin/mbin/azorius/other lesser used instance software will inevitably happen as people only test against the largest player in the field (in the ““threadiverse”” that’s Lemmy, in the microblogging fedi that’s Mastodon). So simply by not picking the largest you’re, even if in a small way, helping not only mbin but all the lesser used fedi software as a whole.
Your own local communities being “dead” mainly boils down to communities themselves having a network effect around them where the largest one keeps growing larger as everyone focuses on it. And the largest communities are usually on lemmy.world (or occasionally other Lemmy instances). There isn’t that much you can do there.
In my experience, it’s always the smaller software that innovate. The same is true in the microblogging fedi (emoji reactions, quote posts, markdown, nomadic identity, reply permissions) just as it’s true in the ““threadiverse”” (combining communities together, the ability to follow people, polls apparently (?)).
So really, don’t worry about the size of your own instance’s communities. As long as you trust your instance’s staff to keep you safe there’s no real reason not to get on a smaller instance, or on different software. Especially on here, where “discoverability” is not as much of an issue as it is in the microblogging fedi.