Aliasing is a thing on Mastodon user accounts. There's no conceptual reason it couldn't be extended groups on other platforms, too.
At the same time, if group aliasing became a thing, one should not expect that one group become an alias of another. Centralizing communities doesn't always make sense, and our Love of Large Numbers is something we should actually actively push back against.
Aliasing makes sense when you have a dozen tiny communities, none of which are large enough to be self-sustaining. Once communities have crossed the critical limit and become viable all on their own, we really shouldn't actually want them to merge with other viable communities. Smaller communities are easier to moderate, are generally friendlier spaces, and the promote a larger diversity of opinion and active, meaningful discussion.
Bigger ones devolve rapidly into jockeying for attention.
If you're only going to read 10 or 15 posts in a community, be it one of 1000 users or one of 10,000,000, then you're generally going to be better off with the 1000. Anything big enough to make it to the top of the big blog will probably be discussed in the small one, too. But the opposite is just not going to be true.