In my opinion, intended or not, this was done to expand the player's horizons outside the story into boss battles that unlock even more content. Unfortunately, getting my rat to 100 was a nightmare and though well worth it thus-far, agreeing-ly quite a random requirement for content so significant past.
I think it's great that most players want to get engaged here. But when it's almost a need when there's alot of content without context, it's definitely quite the balance.