The question is what would happen to/on Monero if it was really used as much as Bitcoin? With tens of thousands of txs per hour? Would it be as decentralized, could people still run nodes?

It is already quite hard to run a Monero full node due to the fact that the cryptography is hard and it requires a lot of computation power (so Pi4 is already kind of too slow). What if the blocks were huge?

If you can only run a node in a data center, they can turn you off.