I understand that Google has a lot of data to shift through, and that maybe the Fediverse probably can't do everything it does.
When a user tries to search for certain things on a search engine it's like Google goes out of it's way to hide a lot of it.
I guess what I am trying to say is the Fediverse is best for finding discussion, and up to date topics, and opinions from more voices instead of the few that gain the seo system. When it comes to local stuff, I would probably use Google maps or something like that just so I can say I don't need a search engine for that, but that's just me when it comes to local searches.
If one server were to get too big and do ads and all that, guess what, it's not like with Youtube for example where that's your only option you can just switch your instance and you won't be censored you just won't show up on that corrupted instance. The fact that the Fediverse is decentralized and federated absolutely will prevent this from being as bad as it was with the og old internet.
The reason Facebook took over was essentially the fact that it was it's own platform, and you couldn't communicate with your friends from that old forum site from Facebook.
When one or 5 servers get to a certain size I would assume some instances would block some of the largest instances, but would still be usable as it could still federate with other instances. The Fediverse designed to combat this type of thing, while the old internet, really had no way to combat this. Sure it thought well for people it just wasn't built to give people enough power to avoid bigger sites from controlling and censoring the entirety of what is said online and still have success and activity.
While email was federated, it was also commercial in most used cases. Actually email itself hasn't really had any big take over or monopoly and emails seem to send even to this day from smaller email services to larger email services. So this seems to prove that federation can prevent what you seem to be claiming if people make the right steps with the tools they have.