I'm interested to read your opinion on that ["Hardlight is more powerful than Armor Lock"] if you want to share it.
Armor Lock - Hardlight
Instant invincibility on all sides - Instant invincibility only in the front, still vulnerable from the sides and back
Destroys vehicles on impact - Does not destroy vehicles on impact, the Hardlight user is killed, even when approached by the front
Recharges health during use - Recharges health during use
Invincibility from grenades - Vulnerable from well placed grenades on the sides or behind the player
Invincibility from explosive weapons in all directions (explosive vehicles as well) - Invincibility only from the front, still vulnerable to any Rocket/Tank shot on the sides or a wall behind them
Can't move around - Can move around
Reflects specific weapon/vehicle shots - Reflect specific weapon/vehicle shots
EMP blast that can be used twice and can then kill after one melee - No EMP effect
EMP blast that can disable vehicles - No EMP effect
Recharges health during use - Recharges health during use
Can look around - Can't look around
The move around mechanic is a huge advantage, but not nearly as strong to offset being vulnerable from all but the front. The movement is slow and even after they get behind cover, a well placed grenade will still take them out. The movement isn't effective if the opposing player has grenades or explosive weapons on him.
Hardlight being vulnerable to vehicle splatters while Armor Lock could destroy a Wraith after one hit is a large difference as well. No longer are we scared when we're about to splatter someone who isn't jumping.
The EMP blast/melee mechanic was overly effective. Regardless of how much health you and the Armor Lock user has, if they are hit by the EMP blast (which means they're close enough for a melee), they have a large disadvantage because only the AA user knows exactly when he's going to exit Armor Lock and time the melee perfectly, especially when accessed to a 360 degree view.
It's been said that the Hardlight isn't as complained about due to other problems in the game. That's not true. In Reach, there were vital problems such as bloom, jump height, and no-bleedthrough (double melee). There's also an argument that there's more powerful AA's to choose from in Halo 4. If anything, Jetpack has been nerfed in Halo 4. The initial launch is slower and the max height is significantly shorter. Thruster is an improvement from Evade. It's less distracting, slower, and the movement is shorter. Camo is significantly buffed in Halo 4. Sprint is no longer an AA. Promothean Vision is a new addition. The Dropshield provided cover and a shield recharge while the Regeneration Field just provides a shield recharge. Though, both of these are near nonexistent in the game. Hologram is buffed in Halo 4. So what do we have on each side?
Reach (more powerful AA's)
Sprint (easily the most used AA)
Jetpack
Evade
Dropshield
Halo 4 (more powerful AA's)
Camo
Hologram
Promethean Vision
Autosentry
The effectiveness of AA's outside of Armor Lock/Hardlight isn't that much different and I can't see an argument that supports Hardlight being clouded by other powerful AA's, which Armor Lock apparently didn't have. Reach had powerful AA's as well but didn't see much light due to Sprint and Armor Lock. When Armor Lock was an option in Reach, at least half of each team was using them (remember Reach Team Slayer).
343 also went out on Armor Lock in a Sparkcast and were literally laughing on how OP it is. They mentioned they would not implement such a powerful AA again and until now, I haven't heard anyone disputing this wasn't the case, at least on the level of Armor Lock.