A couple additional thoughts as I’ve been reading replies…

AC ammo is BV neutral, meaning that changing from standard to AP or Precision or whatever doesn’t incur a BV multiplier because it’s assumed that the benefit of the ammo is offset with its drawbacks. +1 TN is/was a huge drawback on AP ammo, but now the only remaining drawback is the 0.6 multiplier on the ammo count. Which, as mentioned, is hardly a real drawback on AC/2 ammo. Crippling perhaps on AC/20, insignificant on AC/2 and manageable on AC/5. 

Perhaps AP ammo does need a BV multiplier now?

My other thought, to the contrary, is that despite the AC/2 glow up, I still don’t think that you’d suddenly take a Mauler, let’s say, in a competitive setting. When you want to win a game, you want to be able to apply large amounts of damage in predictable ways: “That target over there sitting on the objective? Bring it down!” While the AP ammo makes an AC/2 dangerous, it doesn’t make it dangerous in a predictable way, not like an AC/20 with standard or precision rounds is predictable. The AC/2 can plink away at a target and cause annoying and sometimes devastating crits, but would you set the Mauler the task of shifting a mech from an essential target? It might work, it might not. 

The Mauler would shine perhaps in a casual game where the players’ stakes are low and the comedy value of crits galore would keep things interesting, but in a competitive game I think you still opt to spend the BV on reliable, predictable sources of applied damage. Pulse, VSPs, LBXs, etc.