At melee distance, dual blade's hitbox isn't really that much worse than the others, in terms of leading you into getting hit: As long as you're in the face of a monster, you're going to get hit more often than playing ranged, hence why, for balancing reasons, melee weapons grant "phys damage reduction", or in previous games, having armour sets with higher defence.
You're right that its hitbox is an issue when trying to hit weak points, however, that really isn't the case for most monsters, as they hang their head(common weakness) low. There are few that have weak points too high for dual blades, one example is Diablos. In any case, you should aim for the monster's legs, as many would recommend any dual blade users to do, not only would all your hits connect and that knocking the monster down will give you time to dance on the monster's weak point, but beneath the monster is generally very safe, very few attacks, like jumping stomp, will give you a tough time rolling out of harm's way.
What likely is causing you to get hit more often is that it has a few attacks that you can't cancel out of, and it's easy to get carried away since it's a mashy weapon. Aside from the aforementioned Evade Window and tools, you should also learn your buttons and combos, so you know which exact attack combo to use that would give you ample time to roll out at danger.
Dual blades are easy to get into, but difficult to play well.
