That's actually pretty brilliant. How about this?
"You use your archetype levels in every archetype that grants combat maneuvers to determine the highest degree of combat maneuvers you can learn, determined by the archetype with the greatest access, just as you would with class levels. However, if you have both class and archetype levels that grant combat maneuvers, track each separately.
For example, if you have 10 levels of fighter and you gain a level of Bladesworn Warlock, you may only take combat maneuvers of 1st degree for your new maneuvers known. You must take two more levels of fighter (or another class that grants combat maneuvers, such as rogue or ranger), in order to learn a maneuver of 4th degree."