Cynthia = 1 loss in the anime (only Ash)
Leon = 3 losses in the anime (Sonia, Eternatus and Ash), two of them in the same episode
Cynthia losses to legendaries = 0
Leon losses to legendaries = 1
Cynthia = 2 gimmicks
Leon = 1 gimmick
Full Power (both gimmicks) Cynthia = undefeated
Full Power Leon = defeated
Mega/Dmax Garchomp = undefeated
Gmax Charizard = defeated (0 KOs in the final)
Aura gimmick power-up = used by Ash on Lucario vs Cynthia to allow him to beat Togekiss
Aura gimmick power-up = not used by Ash on Lucario vs Leon
Pikachu = beaten by Cynthia early on
Pikachu = beats Leon, including his 2 strongest with 2 Gmaxes
Ash Gimmicks required to beat Leon = 3
Ash Gimmicks required to beat just DynaKiss = 2
Ash Gimmicks required to beat DynaKiss + MegaChomp together = likely all 4
in short, anime Cynthia > anime Leon