Or has it changed with Luffy growing and awakening his Devil Fruit and with more time passing?
I never did a deep dive into Luffy arsenal. But what I understood is this.
Using full potential of devil fruit (Except Awakening)+Haki Blast (Using everything at once and His haki blast doesn't last more than 10 min)
Gear 4 was built like that.
Gear 3 has Usage limit. (like he can't Stay in g3 forms for reason and he can't continuously keep on making G3 in a battle , it doesn't make any sense)
Gear 2 has Time limit as well , as it start circulating/pumping blood Faster , making him exhausted fast.
Gear 5 (No clue as of now).
Only way luffy has overcome G2 and G4 is
Temporarily shifting to it and reversing back Immediately, we have seen it multiple time in wano. But no idea on how Efficient that it.