TCP/IP is decentralized, but the actual applications built upon it do not require we maintain that decentralization. Even the hosting services or your ISP access to it, limits the decentralization in practice. The important bit is that there's an optionality. Someone can go back to the protocol layer, TCP/IP and start again, built alternatives. #Nostr has this feature. If a centralized set of high performance relays behave inappropriately, alternatives will be incentivized. People will seek them. There is a check to the authority that may be created in having the most popular platform. That is sufficient to keep the internet free, while all the ISPs and platforms misbehave.