Shanks and beckmann among the present duo,
and the perfect representation would be Roger and Ray since Luffy is going to surpass roger and zoro is going to surpass ray(my 2nd fav character surpassing 4th fav character)
That's not how the off-panel fights works. The time between Chapter 1000 and Chapter 1015 is much more than 30 minutes, which was the near amount of time that Kaido soloed Chapter 1010 Luffy between Chapter 1013. Based on this ''only the panels that we see counts'' logic, Kaido vs Luffy fight also lasted less than a minute.
King said he can't help others because he was busy in Chapter 1004, he meant Marco soloing him and Queen ( In Chapter 1005, we see King was fighting Marco), thus he couldn't go to kill 9 scabbards, instead others went to finish them.
Also note that Marco was clashing with Big Mom for unknown amount of time (between Chapter 992 to Chapter 995) while Kaido was soloing 9 Scabbards. That would also reduce Marco's stamina.
Marco fought King + Queen for most of the time, and did so while healing the samurais from Queen's plague.
Of course, fighting 2 elite YC's and using their power to heal an army will obviously drain all of their stamina, resistance and power.
Marco's goal in the war was always to be a support for the members of the new generation to shine. From the beginning of the war, Oda made it clear that Marco would be someone powerful who would act as a great supporter.
The title wings is actually like sweet commanders or calamities. Remember when Jack was introduced ? "One of the closest man of Kaido-sama". It's just the title for the strongest and most closest men of their captains.
lets pretend like zoro never went all out until onigashima's rooftop battle.
lets pretend like zoro wasnt fighting an admiral in dressrosa albeit for a while.
lets pretend like enma didnt give him a major powerup.
lets pretend like zenkai boosts dont exist.