Apoo was PIS of a non serious Luffy, a Monet situation to stall out the serious confrontations with fake drama.
Boro breath wouldn't have stopped Boundman Luffy as we saw later in the chapter- and that was a team effort of Zoro and Law. Heavenly fire wouldn't have done anything major either.
Zoro was the one who dropped Luffy and claimed it as his incompetence- reread Zoro's statements, this was PIS for Law not teleporting Luffy away to recover anyway, instead giving exposition to Kidd.
Luffy dodged the slashes with G4 speed, not Zoro blocking for him. Zoro was blocking the slashes in his personal space, in 1001 Luffy is IN FRONT of Zoro. If Killer can fucking dodge these you don't think BOUNDMAN can? how bad can someones takes be lol.
Luffy warned them all of Hakai using FS, without that all of the 4 SNs apart from Luffy would have been hit, that is manga fact, whether or not Luffy could have avoided it himself had he not wasted time warning them, we'll never know, but I would assume so given he is the fastest character on the roof, to the point of shocking Killer in that same chapter doing a double take that Luffy already was engaging Kaido when he thought he was next to him.