People joke that Aquaman is useless, but
that's only because he's so good at his job
that you don't even realize he's doing it.
What is his job? It's making 71% of the Earth's
surface completely inaccessible to his enemies. If
you have Aquaman on your side, your enemies can't
go anywhere near any body of water without you
finding out exactly where they are, and if they even
have a fishtank, you have a constant source of
intelligence on them. We don't see a lot
of battles that take place in or near the water
precisely because no villain would dare set
foot into Aquaman's sovereign domain and so
they are forced onto land where the
other heroes can deal with them.