Surely in Europe and US there is lot of nodes, but it’s not about geographic centralisation, it’s more about power centralisation, 2 pools own around 70% of the network wich is not so good, but supposing 51% attack, they will be able to validate their own invalid transactions and reject all others transactions, they will not be able to selectively block transactions because every transactions is anonymous. But in Bitcoin, if 51% attack happens, they will be able to selectively reject transactions, like in Ethereum actually. The main difference is if Bitcoin become overtaken, many people will don’t care because they will be able to transact normally, but Bitcoin will be compromized... hope Bitcoin will go in the privacy way more in future 😉