Okay so I have been playing still. To the Arc apologist, I did unlock the Arc upgrade, I still don't think it is that good for all the reasons I stated. Too narrow a goldylocks zone, stun is not effective vs bigger stuff, too finicky
Now if you want an under appreciated support weapon that shreds, pick up the LAS-98 Laser Cannon. It fills all the same niches as the AMR, it deletes hulks when paired with stun grenades, it scrubs out devastator heads in an instant, it is probably the best weapon against gunships in game. Against bugs it struggles vs Chargers (like the AMR) but wipes the floor with Spewers (like the AMR) and fairs well vs the rest. The downside is the lack of utility (like the AMR).
Basically if you are bored with the AMR the LAS-98 is actually quite viable now and fun.