Ah, I get it, they're both lance kings. Clev-Whoa, I just gave myself deja vu.
Joking aside, clever option to keep the theme going for this FE VS DC string of fights.
Skill isn't as huge of a differance here as it was in Eirika VS Wonder Woman, not only is Ephriam more combative than Eirika is, Aquaman isn't quite on the same level as Wonder Woman in experience just yet, so I'd say comparing thier major battles these two should be much more equal, and I don't know who would get the edge.
Same thing with AP, like on the other thread the DCEU's Country Feat is really close to Sacred Stone's Country feat, so I'll assume they're either equal or the differance is negligable.
But when it comes to gear and powers, the tides have turned (Ha, I'm hilarious). Ephriam's only range is the Javilian, he has no easily retrieved ranged weapon or one with magical abilities, so his ranged abilities are really hurting. Not only that, without having magical weapons, Ephriam has a lot less powers at his disposal compared to his sister, in fact the only 'power' he has is a selective soul manip that Aquaman is probably immune to. Meanwhile, Aquaman can effecitively fight on both land and water (assuming SBA, he can use the water in Central Park for example), while Ephriam has no history of fighting in the water, so either he'll have to take a disadvantage by going in after Aquaman, or try to lure him onto land where the advantage is nuteral, Ephriam's never getting a positive battle position here.
There's also the fact that Arthur has energy attacks and water manipulation to use for ranged attacks ontop of being an expert up close, meaning Ephriam's going to be regularly outranged here.
I give this fight to Aquaman, Ephriam has almost nothing he can do here.