I've played 2 campaigns that went from 1 to 20, both became a chore late game just trying to keep track of all the items and threads. IMO, a game should stay bound to 2 tiers at most (the tiers being 1-4, 5-10, 11-16, and 17-20), going from peasant to world ender is just too much baggage. Maybe 3 tiers if you do want a complex and difficult to manage, but still possible to manage end game.

Extra credit here being that you are a shit load more likely to actually complete the story you want to tell