You're right you earn crypto keys based on how well you play per game. But it's common sense to know that if you're leveling faster per games you're missing out on crypto keys per level.
Normal: I earned 4 crypto keys playing CTF and gained half a level. Double EXP: I earned 4 crypto keys playing CTF and gained a whole level.
Thats all I'm saying, it's basic common sense to understand where I'm coming from lol