Let's have him arrive in the way he did before, not in time to save lil Oarz Jr.
The problem I have with this hypothetical is that if Luffy arrived with gear 4th from the start he'd be to the platform much sooner, or would attempt to be. The events aren't going to play out exactly the same, step for step.
- Chapter 557: Luffy arrives, stops Croc's attack on Whitebeard
- Hypothetical: Luffy arrives, stops Croc's attack
- Chapter 560: Luffy is probably a third to halfway running across the MF bay, recieves the key from Hancock
- Hypothetical: Luffy has gone gear 4th in haste and makes a beeline for the platform, doesn't recieve Hancock's key from below
- Chapter 561: He's stopped by Mihawk, who is intercepted by Vista. He proceeds to run towards the plaza.
- Hypothetical: He's stopped by Kizaru, who is intercepted by Marco. He proceeds to fly towards the plaza.
- Chapter 562: Squardo attacks WB, a handful of people look on in shock.
- Hypothetical: Luffy happens to be using FS, notices in advanced, but is at the plaza by this point and can't alert WB let alone stop Squardo from such a distance. WB is still stabbed.