You can use git to backup Obsidian for free, it works on every device, even iOS.
And that's where Obsidian is "obviously better" than notion, it has plugins that anyone can develop.
Another reason why it's better, which is also why it can be so easily backed-up to git, is that it uses simple markdown files with 1 file = 1 note. If Obsidian stops working one day for.. reasons? You still have all your notes and can use any markdown editor to use them.
And that's where Obsidian is "obviously better" than notion, it has plugins that anyone can develop.
Another reason why it's better, which is also why it can be so easily backed-up to git, is that it uses simple markdown files with 1 file = 1 note. If Obsidian stops working one day for.. reasons? You still have all your notes and can use any markdown editor to use them.