Ok, the rooftop was obviously a supernova only thing for thematic reasons. After that, the rooftop gang disassembled and went to their real fights. Luffy vs Kaido, Kidd and Law vs Mama, Hawkins vs Killer. Let's not pretend being on the roof was a power level. The story directs it and was better for it, but even if Akainu, Sabo, and Whitebeard himself were there, thy would never have made it to that rooftop.
As for getting "clapped by Black Maria", this chapter is literally a rebuke to you.
You are literally, legitimately, 100%, doing what Black Maria is doing and getting smacked down for in the chapter that you're commenting on. It's bizarre.