Overview
APC9K is an SMG with a very HG-esque Skill if someone else than her is the Echelon Leader. If she is the Leader or there is no Leader, she simply works like an Evasion self-buffer. She also gains up to 200 flat Evasion based on how many times the Leader hits a target during her Skill. If she reaches the max Evasion from this, she buffs Dolls on her tiles with 20% Damage for 3 seconds (this is a tilescan, and you can see the affected tiles visually when it triggers).
180% Evasion isn't that outstanding by SMG standards, and if you actually want an Evasion Tank you could just go look at Suomi's Mod.
As such, APC9K's main appeal is the massive RoF buff for the Leader. 40% RoF is very high, with a 5/8 uptime. This Skill lends itself directly to Exodia comps, and as such APC9K would mostly fit in to use with
M4A1 Mod or Hanyang Mod.
The flat Evasion buff stacks up really quickly, and combined with her base Evasion and equipment, she should easily reach 300 Evasion very quickly and stay there, provided the Leader keeps hitting targets.