1) During the war in his flash back they mention him to join the schichibukai...He turned it down, and fought jinbei leaving it to a stalemate for 5 days (only a rookie). ( Ace's weakness too x4 logia/fire)
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In fact Ace fell afterwards, before the arrival of WB
The bounty i'm not entirely sure
2) Ace sacrifice himself to save luffy, even you are aware of that also akainu said it himself. His "defeat" during the clash is based on superiority of devil fruits Example: luffy vs Enel...
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3) Luffy generation was not rated the strongest but the most dangerous, they were too reckless and you have to include blackbeard too. You saw what Ace did to blackbeard, even shanks thinks blackbeard is a dangerous/powerful individual.
I'm also not going to say WB trained Ace, just look at all the pirates he was sent to fight that became WB ally.
If you look at the skypie arc, the front book showed ace fighting G-2 alone, while looking for blackbeard.
Luffy trained with Rayleigh, but there still people out there that think luffy is the 4 strongest supernova...He trained in haki, and he still yet to say he is stronger than Ace.
Just look at the baquo works, he destroyed like how many of their ships with a single punch.
Luffy can't even do that yet.