Honestly, I think this is how he's gonna fight going forwards. Like until EoS. I feel like the difference between Base/G2 and G4 isn't that big now and Luffy only uses it for some attacks. It wasn't viable for long battles to begin with. I don't think it being base Luffy makes much of a difference now tbh.
recently it seems that he didn't always do that i think his DF is about to awaken so he will be able to gigantify him self without air. his DF is none other than gigantification DF, that is why he never was able to produce rubber, the air was just a catalyst to gigantify his body. his DF was always odd it is called rubber rubber fruit but he never produced rubber,his DF is an exception every other DF that is named after an element or material can produce that element or that material. so it is getting clear it is the DF,that the Gorosei are talking about. its awakening can gigantify other beings as well, that is how Zunisha came to existence in the first place. so they feared that DF and changed the name.