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Everything was just a series of boss battles. Which isn't a bad thing. It's just that each had a conflicting path to power that got worse the further along each path you went. To the point that if you wanted to "progress as you go" results in you being under leveled and over leveled for everything.
"Event" based level scaling like how Pokémon has always done, it would just be a tad more complex to account for the various path "events" you completed, with the highest being the one to lead scaling for everything else. That way everything stays roughly proportional while still scaling higher as you clear out the other paths. The specific numbers would be up to the devs, but generally it would accommodate everyone without serious micromanagement.
I'm just surprised the Devs haven't figured this out yet.