Marco seems to be the strongest of the alliance. It was already implied when Big Mom herself implied it would take too much effort for her in case of a fight against Marco, and now he is fighting 2 calamities for a very long time now, yet they all have similar level of injuries suggesting the fight to be relatively even, when WCI Luffy was roughly on the level of Big Mom's strongest commander. Though he learned advanced haki down the line, but G4's timelimit will still fuck him up against Marco who is the king of these kind of battles with his regeneration. I assume though that the rooftop guys will grow in the fight, showing the power of the new generation