What makes you think he isn't so strict with Shonen rules? Naruto got his KCM before the war arc. Nothing says Luffy won't get PUs anymore.
What major PU will Luffy even get for Akainu or remaining top tier that's not Teach and Imu?
Luffy is already maxed out
Skyplit like Roger, Shanks,
Adcoa like Rayleigh, Roger
Fs like Shanks, Kaido
Awakening , something not even yonko with dfs have
All Luffy needs is to master his awakening and get PUs linked to VoAt and new whatever PU for Imu & Teach