Imo, it's definitely a win for the Yonko... there's no contest.. with Kaido and Big Mom in Onigashima right now, they're unstoppable, even with all the alliance combined.
However, in my view, I'm certain that the SH crew and the alliance aren't gonna take part in this raid on Onigashima; Oda took steps dismantling the ships, and even the sunny... for what purpose would Oda do that, only to still get the alliance to Onigashima, and make that event redundant in the end?? :unsure:
I believe Oda is using the scabbards as sacrifice, to liberate Wano from Kaido and Orochi... This is why Oda took precautions to prevent the alliance from heading to the meeting place, and made them unable to proceed. Meanwhile, 7 out of the 9 scabbards are heading there, unaware of what was going on..
Wano will be the main battleground for the final fight, not Onigashima... and like every island involved with the SH crew, Wano can't just be the spectator in this war.. it must be the participant in this war; the country must take part, revolve in chaos, and shed its own blood in this fight...
As it is also a betting thread, I'm gonna take a bet and place a pretty big prediction on here: All of the scabbards will "die" in Onigashima, and only two will remain - Inuarashi and the traitor.
Inuarashi's role is to escape to Wano and relay the message of what happened in Onigashima to the alliance, whilst the traitor - whoever it is - will get the chance to redeem himself later in this arc.