It would be horribly frustrating to new players to keep everything as hard to get as it once was. Sure, horses used to be a kind of status symbol - but what kind of status do you still get from "I cleared this outdated fight 3 years ago" compared to "I cleared this current hard content"? Besides, as many people have mentioned, it's really nice that you're having fun doing everything synced! Some others might not! Current content cannot be unsynced so just let people do old fights however is fun to them. You're really not losing anything, and you can always be your fc-grandpa and tell the story of how you cleared Titan ex back when it couldn't be unsynced.