You can just stick with one archetype and stockpile Hero's Leaves to use to rank up everything else. I was constantly leveling up stuff that I never used and didn't even need as a pre-req for something else, simply because I would hit the 99x storage cap otherwise.
The only thing that really bugged me from a QOL perspective was that I felt like I had to use only the new characters as they joined, because the old ones were already ranked up and had the full-XP perks unlocked. Especially since the new characters were way behind in level too.