well with arrival of Shanks now they have WB, Shanks, Ben Backman, Marco, ...
but the Marines coulp potentially deal with that with Akainu, Aokiji, Kizaru, Sengoku and Garp it would be way more intense and it would have been a much more equal fight
if Ace didn't die WB would have never gone into a frenzy
BB, I think, would just chicken out
Akainu was tired , so he gets taken down by Marko and Vista.
BB wouldn't have showed up ( If he would then Mihawk would have fought him and killed him , Yami BB got stomped by a near dead WB )
Shanks would have teamed up with WB and take down Sengoku and Garp ( if they choose to fight )
Mihawk would have probably left.
Croco would still fight.
Jimbei would still be unharmed.
Ace would still be unharmed.
Hancock would protect luffy.
Ben beckman would have fought Kizaru.
The other member of Shanks's crew are probably strong too ( the ones that showed up in the stand off against BB) so i believe 2 of them can take down an Admiral like Aokiji.
Not to mention that WB wouldn't have had half his face blown off.
And we forgot Jozu too , basically its a mid diff for the two Yonkos U_U