Or all the other tacticals, really.(To be fair here, I have used A-wall exactly twice, and hated it both times. I've probably spent less than 10 minutes using it).
TL;DR: Since the Devotion and Hemlock were so powerful, so was the a-wall. Now that they are nerfed, a-wall is not as powerful. Therefore, it doesn't deserve a nerf.
The problem with A-wall wasn't that it was powerful, it was that the weapons behind the a-wall were powerful. Looking at you, Devotion and Hemlock. Now that they are nerfed(or soon will be), a-wall won't be as powerful. Its power level is artificially inflated or deflated based on the power of the guns behind it. For example, a kraber isn't nearly as powerful behind an a-wall as a DMR because you have to lead your shots for the OHKO(One Hit Knock Out). Now(or soon), it will be just as powerful as the other abilities.
There is an argument for why phase shift is overpowered, so I'll address that too. If you were here for the A-wall rant, you can leave.
TL;DR part II: All the tacticals are powerful and balanced(except holopilot), so there is no reason to nerf them.
Phase shift is my most used tactical, and I frequently build loadouts around it because it fits my playstyle perfectly. This might have a little more bias to it than my previous rant.
One argument against phase shift is that you can move around without being hurt. Honestly, if this was the only reason you thought phase shift was OP, try cloak and low profile. It works almost as well for moving around, but has twice the uptime.
Another argument is that phase shift allows you to easily win 1v1 engagements you weren't supposed to win by giving you a get-out-of-jail-free card. In practice, this only works with fast regen, but essentially this is the main reason to use the tactical. Stim and grapple get you across the map in a few seconds, but stim has healing, so it has one charge, and grapple has delayed speed, so it has 2 charges. Balanced, in other words. Cloak makes you invisible vs. titans and almost invisible vs. pilots. Pulse blade gives you free wallhacks. A-wall is a free amped weapons for 6 seconds, and lets you be invincible 25% of the time(side and behind engagements are not helped with a-wall. Holopilot, is, well, completely useless. Ignore it. My point? All of the tacticals are powerful. That's how it should be. That's why your pilot image changes depending on your tactical.
The real problem with phase shift is that it has no counterplay. Wrong! You leave a trail of phase-shift-like mist every time you use it, leading to your exit point. You can tell if they disengaged completely, went behind you, stayed in the same place, etc. Now, this trail only goes on for about half of the total travel distance when phasing, but it is enough to predict where most people will go. Smarter players will change direction so you can't tell where they are going, but that wastes half of the ability. Although phase shift barely has any counterplay, the same goes for every other ability. A-wall blocks one side, but you can hide in a corner. Stim has delayed healing effects. Grapple, has slow acceleration, making it harder to escape from areas, so you have to pick your battles. Pilots can see cloaked pilots if they look hard enough. You can shoot at the pulse blade, but you can also throw it to make that hard/impossible. You don't have to shoot at the holopilot decoy, making it useless. Disregard it.
Tactical abilities just depend on your playstyle. The only thing that would help balance them more is to please buff holopilot (a suitable thread title I guess).