> As long as people eventually reach the same conclusion about which chain is the legit one it's fine

What? No, it very much it isn't. Consensus needs to be ongoing, within a handful of blocks (Monero locks transfers for 10 blocks for this reason, called "confirmations").

https://en.wikipedia.org/wiki/Double-spending#Decentralized_...

https://www.getmonero.org/get-started/accepting/

Firstly, I think you underestimate how quickly good faith actors with slightly different configs would come to agree. A handful of blocks should be enough. Secondly, if reorgs start becoming a problem, exchanges and merchants could monitor for a situation with two competing chain and temporarily suspend processing. There is still the possibility that some one will suddenly reveal a long chain they had kept secret, but anyone doing such a thing is very suspicious.