Sure, Apple Notes may have native window resize, but can you tell if the app is syncing right now? When was the last sync? What happens in case of a versioning clash? Will it decide to work with patchy Internet on that upcoming train ride? Will it sync once you go back online? Will it decide to party with some random Exchange server you used for work once, and how will this affect your notes? Are your notes safe from random changes in formatting when Apple rolls out improvements to the Notes app?
Don't get me wrong, I love my iPhone and have used Macs for decades, but I wouldn't trust Apple cloud services with anything even remotely important. I'm even a little sceptical about Mac Finder at this point, which is ten minutes away from becoming a cloud service itself.