No, it sounded like you were saying you wouldn't do two arms at once.
When superfluous I would not.
Most WC, from my point of view, does secondary actions as a first response, violating all 3 of the core principles of VT fighting strategy.
But what is clear, is that you have a much narrower view of what "LSDD" refers to that everyone else here. I see it as having several layers. One of which is defending with one arm while striking with the other at the same time. Another is defending and striking at the same time with the same arm. Another is angling off-line with a strike at just the right moment so that you don't even engage the striking arm at all.
Your 1st idea is simultaneous attack and defense, but LSDD refers to a single specific type of action that simultaneously displaces as it strikes. That is the unique skill and tactic of VT, hence the maxim, further spelled out by "
da sau jik si siu sau". The striking arm is also the neutralizing arm. Can't get any clearer than that.
Even when using a helping action, the striking arm should still possess this dual function in case there is further obstruction along its path. That is LSDD still referring this quality in a single arm.
You call it narrow. I call it clearly defined VT strategy and tactics. You get that in a coherent system. Ambiguity in core concepts is for the confused.
Your 3rd idea doesn't work because
siu means to eliminate, to dispel, or to remove. This requires acting upon the limb. Dodging doesn't accomplish that.