No, it is never described as a MOD, it is explicitly an attribute itself, but you still modify (in the dictionary sense of the word) your roll with your ARM value. In game terms, a MOD needs to modify the attribute so the highest effective ARM a Jotums can have would be 22 which is 3 Booty rolls of +3 and Cover. Simply treating ARM and BTS as a MOD would actually put an effective cap on ridiculousness that could occur, though, and those values really do snowball hard at high levels.
As someone who interfaces with new players, my response would be: This is why the Crit mechanic exists. This is one of those circumstantial opportunities where tying something up in CC can be very worth it. This is a good time to utilize BTS-based attacks (especially Viral, E/M, or Breaker) as opposed to going versus ARM. This is (as mentioned) the best example in the game for including K1 in a list. This is a good example of why Order hunting and backline attack is often easier than attacking a tough target head-on. This is why playing to the objective can be more important than individual piece removal.
