wise prophet
All Star
It has nothing to do with non-fruit users being incapable of getting strong, it's pretty simple really.
Ace vs Sabo was dead even...
Ace got one of the strongest devil fruits and became a logia after already being an equal to Sabo..
So Ace was Sabo's equal and then he got an upgrade. Therefore...My assumption, Ace = Sabo but Ace + Mera Mera Fruit >>> Sabo
Don't forget that Sabo spent years under Dragon and the Revolutionaries before Ace even left Foosha Village. By the time Ace was 14 Sabo was probably already a bit of a beast