There must be some part of the attack I am missing here. Let's say I'm an attacker and I do this. But now none of the subsequent blocks on the original chain w

There must be some part of the attack I am missing here. Let's say I'm an attacker and I do this. But now none of the subsequent blocks on the original chain will validate anymore because of hashes mismatching. I could of course validate new blocks but 6months+ of blocks from only one or a small number of validators (depending on how much validator capital one can amass for the attack) is going to be pretty obvious. Unless the attacker can get a significant percentage of validators part of the attack, I can' see it work out in practice.