Bitcoin is censorship-resistant for now. But what if big companies, governments, and institutional firms run their own nodes and/or miners? Since they have a lot of capital and resources, they can make a big difference on the network. And with mining pools being centralized, we should expect the worse.
Nothing would change. This is not Ethereum and this is not Solana. The amount of resources and concentrated, sustained effort that would require to censor a network like Bitcoin is ridiculous. It is not even worth a consideration at this point of time other than in what if discussions. These things are funny because there is always FUD. If the big guys are not involved, then it is bad for some reasons. If they are involved, then it is also bad for some other reasons. There is never a "things are fine how they are, at least for now" scenario for people who succumb to FUD.
I believe solo mining is the only decentralized way to truly-defend Bitcoin against a 51% attack. But I could be wrong. Developers can come up with a solution to prevent mining pool centralization, though. That way, Bitcoin will be more resilient against manipulation from "big players".
There are no good ways that you can force people into solo mining, and as such this technique offers no protection against a 51% attack. You can solo mine, but you can't force others to do it.
Governments and institutions are amassing a large portion of the circulating supply with the hopes of "owning" it all. So long as the rest holds a greater portion of the supply, there should be nothing to worry about.
There is nothing to worry about, at least for now.