I'm not saying Calling is absolutely terrible, but I think its worse than 3betting imo depending on who youre playing. By just calling (esp OOP) youre putting yourself in a kinda bad spot. By just calling you've left yourself with not so much information regarding the villians hand, and what do you do when he fires the flop? Call=? raise? Does he fire multiple barrels with air? etc etc i think you get the point. Overall calling just puts you in a bad spot.
I'm very very aggro in HU. Lets say youre only 3betting 5% of your range, in HU thats super obvious. Are you raising every button? It seems since youre def. not 3betting as much as you should that you're probably not raising as much as you should from the button also. I raise pretty much every button (unless my opponent adjusts) and play my position pretty aggressively. HU is all about adjusting to the player, if the player is going to let me run over them, than I will. If the player starts 3betting me and adjusting, than I adjust
In HU you gotta mix up your game, and you cant play really ABC. (At least against good opponents).