That's important imho. Since most attacks will come from right handed people, we trained almost exclusively with right-handed defense.
In my grappling art, since most attackers will be right handed, you will need to be most proficient with right hand defense. That doesn't mean only defending with your right hand, it means defending against a right handed attack. It makes sense to learn a few left handed attack defenses, but that shouldn't be your concentration. I think that would be counter productive when the majority of attacks will be right handed.
And right hand attack doesn't mean only the right hand/foot will first attack you. For example, a person may grab you with his left hand for control preparatory to striking with his right hand.