Current Luffy would Molly-whop Doffy but that's a debate for another day. Luffy decided to enter G4 because he couldn't break Ulti's grip and he decided to use it after knocking PO with G3 and immediately after announcing that Ulti is strong so the notion that he used it only because it was two on one is moot.
In a 1v1 Luffy would have blitzed and taken her down. Then what happens? No PageOne to distract him so he can just give her an Elephant Gatling. Contrast this to Dofla who was laughing at G2/3.