Hey James! Great question (and to be compared to Kevin Crawford's work means a lot)!
I thought a lot about how many levels to provide each class. Since I envisioned Wandering Blades as a toolkit for wuxia movies and for the combat to be highly lethal, I opted for a lower maximum level.
That said, even with the the current exp system, you can still engage in a longer form game (if the characters survive) if you include martial arts manuals. Rules for these aren't in the quickstart, but to put it simply...they enable players to trade exp for martial arts techniques! This way, you may have lower level characters with powerful techniques fighting alongside higher level characters with standard ones!
If you have any other questions, please don't hesitate to post here or on the Wandering Blades Discord server: https://discord.gg/y4C3vynp8q