I find the strategy of abandoning the field of debate and retreating behind a "2nd Amendment" mantra to be a dubious one,
There is a difference in abandoning the field of debate, and choosing to play on the proper field. Which in the case of a loaded question such as "why does anyone need to own an assault weapon anyway?" is the proper choice. No matter how much utility you ascribe to an AR via what ever reasons you think give it utility does not mean someone else will see the same utility. It's entirely subjective.
You may think all those reasons make it so you need an AR, but in fact they don't. Every single function of need which you have proposed is in actuality a function of preference. We need oxygen, we need water, we need food. To shoot a target, a threat to your life, a deer, a squirrel, a moose, a bear, a whatever, sure an AR can do the job, but so can a lot of other firearms. If there are a multitude of alternatives, you may want it and find it preferential, but you don't need it.
Sure you can play football on a frozen pond, but that doesn't make it a wise venue to do so. Similarly, attempting to explain how you "need" that AR with a list of utility that is completely subjective is not a wise approach.