They have similar alphabets, grammar and a lot of cognates. If you only spoke one you’d be able to recognize most of a sentence with these things, but sometimes words are totally different. They probably sound similar to someone unfamiliar with both, but they are quite distinct.
I think they’re hated because they’re synonymous with broken group chats and low res photos. Hopefully EU forcing rss adoption fixes these instead of having to download an app to ‘fit in’.