2 seconds is MORE than enough for what his trait does, lol. Lemme explain it a little better.
The trick to using his trait is basically using it like an MK breaker/Guilty Gear burst that ONLY works on ground combos. If you do a move that you expect to get punished by a ground string (whether on block or whiff), you wait and watch to see if the opponent hits you with such a string, and when you see your character get hit, you IMMEDIATELY pop trait and start blocking. (DON'T hit trait BEFORE you see your character get hit. That's just plain inefficient.)
It only lasts 2 seconds, but you're only gonna be in hitstun for, like, 1 second NORMALLY. That's BEFORE you trait and gimp the HELL out of the hitstun your opponent can put on you. Even in the fastest-hitting 11 strings (and multi-hit specials such as Deathstroke's guns and Aquaman's Trident Rush), 2 seconds of highly reduced ground hitstun is MORE than enough time to block and avoid or SEVERELY reduce otherwise guaranteed damage. If you escape such a combo with trait and manage to block before getting launched, your trait has done its job. You ruined their punish, and depending on what you traited, you might even get a punish of your own.
The cooldown is minor as well because Aquaman is SUCH a strong character at neutral. If you escape a combo with trait, chances are good that your opponent is going to get very frustrated (because they didn't get their otherwise free punish), very predictable (they knew you were going to trait but they have some angle to try and beat your defense), or both. This all plays into Aquaman's EXTREMELY strong block-anti-air-and-whiff-punish game. If you are a solid player, it's EASY to defend yourself for 8 seconds before your trait comes back up. Most of the stuff that will break your guard as an Aquaman player can't be traited anyway (throws, for the most part).
If you need a visual example of the ways you can use his trait effectively to defend yourself, I highly, HIGHLY reccommend watching the stream archive of the ECT top 8 from this year. Tom Brady's Aquaman does a GREAT job of using trait to save himself in situations where he'd otherwise get blown up.