I think it would be pretty difficult for Lemmy/Mastodon/Kbin to become bigger than for-profit counterparts. For-profit businesses can raise loads of funding and spend all that money on lots of engineers to refine their platforms.
But I do think the fediverse is pushing big tech to alter their platforms. E.g. Meta planning to support ActivityPub in Threads.
But that was obviously based on nothing factual. If Reddit could grow to that size without turning a profit (and by exploiting free moderation for its labor), why wouldn’t any fediverse site be able to do the same? The truth is that the the content is what drives growth. If the fediverse has the content, people will go to it.