It's not a reddit clone just because you can aggregate content, that seems like a rather narrow view. The instances could still host their own communities and the supercommunities could exist alongside one another and choose which communities would be part of them, it would just be a functionality that perhaps some users would find helpful. Wouldn't even have to be on Lemmy but for example on kbin or another alternative.
Why is that necessarily a bad thing? Wouldn't it increase the usefulness of federation since it distributes the data but allows for the communities to remain connected to each other? Couldn't you just not partake of that feature if you're opposed to it?