Hardlight shield has a lot of issues that I don't like.
Similiar to Armor Lock, it pauses the action and allows a player to slow down the pace of an encounter at the push of a button. Yeah, if you have a teammate nearby and they don't, its not really a hassle. However, in a 1v1 engagement, it dramatically slows the game down and shifts the encounter to their favor, just by pressing a button. Not only does it allow them to block projectiles, but they can move to cover while doing it.
While a grenade would usually be the solution, Halo 4 has taken some pretty dramatic steps to limit the amount of grenades a player has at any one time. If you're active and agressive, the chance of you having a grenade when you encounter someone with a HL shield decrease significantly.