This train of thought will inevitably backfire, sooner or later.
Luffy cant defeat both, that much is guaranteed. Heck, he cant defeat one without help...
So, if they both get defeated here, Luffy will miss out on one.
If none get defeated here, Luffy wont be the first to beat neither Admiral nor Gorosei.
And yet still the fact remains that Luffy's subordinates have never literally taken over a fight from an enemy Luffy has not defeated on his own.
I think its without question that one or both will be defeated this arc, and if thats the case, the cause of their downfall will almost certainly be Luffy.
This is why Ive stated that I expect Luffy to defeat an Admiral, and not necessarily the Gorosei, because yes it IS hard to believe Luffy could fight both. And yet, Oda still leaves the damn robot lingering....
If neither miraculous get defeated, then it doesnt matter, because by then Luffy will be fighting Akainu and Imu, stronger iterations of the people under them. The relevancy about the current arc where it happens, i.e.
If Luffy didnt defeat YCs at WCI, then it does not matter if Sanji or Zoro defeat them at Onigashima, because Luffy defeated a Yonko
Same logic here. If he doesnt defeat them, no one will. If they get defeated later by his subordinates, Luffy is fighting stronger people anyway.