G4 is basically ballooning his muscles with air and holding it with haki ; hence luffy can't let the air go from him
--That is not the case though. Sengoku's DF is also a human model. The animal form will also be human like in itself. We don't know whether he used hybrid or full zoan mode but there won't be any difference.
--The difference between sengoku's fruit to Luffy's is that Nika mostly looks like a ordinary human.
--Also you are confusing awakening with hybrid or zoan. Every zoan from the start as hybrid and zoan modes but because luffy's model in nika looks like a normal human it doesn't matter whether he is in base , zoan or hybrid -- All of them looks same.