Except that as you say, it's too expensive for every node to have a full copy, so there will only be a few dominant players. If that's the case, web3 will be like what we have now, where instead of the dominant players being Google, Meta, and Amazon they will be the two or three dominant web3 companies, with a few smaller people trying to keep up.
You are massively over estimating how much a copy of the entire history of ethereum costs.
You can store the entire blockchain on a 1 tb harddrive.
The cost prohibitive nature is only running an open rpc that you tell hundreds of thousands of people about. Then you will have to deal will letting all those people access that 1tb of data.
Quicknode lets you have a private rpc with the full history of the chain for dollars a month.
That's not how decentralized blockchains work, you participate in staking or as a validator, there are no "companies", it's open source and decisions ar3 made from the ground up, meaning your are a participant. Also to say every node needs a full copy is about 5 years behind what's currently happening in the space.
So I would agree with your last sentence.