I don't think he's saying its hard to kill ack. I think he's seeing the same issues I am, that nearly every hit registered seems to be lethal. I've been chalking it up to lag/net issues. I'm guessing that my FE isn't registering the hits immediately, but catches up a split second later, effectively giving me all the damage simultaneously. This could be completely inaccurate, it's just a guess. I've noticed my connection has been incredibly poor lately, compared to several months ago, so I'm under the assumption that delay is a culprit here.
FWIW, hispano armed planes will kill an ack with 1 or 2 hits anywhere on the pad- a 2 second burst is serious overkill.