SPOILER TALK
First, wasn't surprised by Aquaman winning, not that I doubted Arthur could win... just that THAT seems to be the rule with 'Death Battle' Marvel vs DC fights anymore.
My problem is just in the way they figured he'd win....
Didn't the effect of 'Aquaman's Telepathic 'PING' Ability' and whether it'd really affect Namor get answered by JLA/Avengers? During the big final battle with Krona, Aquaman had to use a massive sonar/telepathic attack on a whole swarm of aquatic enemies, despite knowing it'd effect Aquatic allies as well, and the only one left standing was Namor... albeit with a massive headache.
I bring this up because JLA/Avengers was the biggest source used for the 'Thanos v Darkseid' battle for the Infinity Gems conundrum. The 'Cause a Hemmorage' ability displayed in the Hyerclan storyline of JLA came some time before the JLA/Avengers crossover... and one could assume this was something akin to what Arthur used to put down so many Aquatic foes in one go.
And again... Namor was still standing.