I think you make your own argument too complicated....
The militia clause is not operative. Therefore, whether or not a weapon is used by whatever the militia might be is irrelevant.
The 2A is a fundamental right.
The militia clause is not the operative clause.
"The right of the people to keep and bear arms shall not be infringed" is the operative clause.
The standard litmus test is:
1. Does the government have a compelling interest in creating the law?
2. Is the statute as "narrowly tailored" as possible to meet the compelling interest?
3. Are there less obstructive/restrictive/intrusive means of accomplishing the same objective?
Banning semi-auto anything or particular rifles of any kind is not "narrowly tailored" nor is it the least possible intrusion nor does it meet the objective in some unique way.
Therefore, it is unconstitutional.
Still happily answering to the call-sign Peetza.
The problem, as you so eloquently put it, is choice.
He is no fool who gives what he can not keep to gain what he can not lose.
-Jim Eliott, paraphrasing Philip Henry.