Personally, what I think the flashbacks was missing most was any sort of defining point that made Ace and WB want to make the other one the pirate king.
I agree. I think everything else was fine though. Especially the scene where Whitebeard and the rest of the WB Pirates were telling Ace not to go after Blackbeard.

Also the present scene where Marco agrees that Whitebeard did send Ace out was awesome. I have a lot more respect for WB and the WB Pirates as every chapter progresses. Their brotherhood is otherworldly it seems.