It's not the marbling that affects a 'cube' steak's tenderness..
It's the white streaks of connective tissue that many consumers mistake for marbling.
No amount of tenderizing is going to make sinuous connective tissue palatable.
I had to educate my own son about that a few years back when we were getting enough tenderized steak for about 15 of our family.
Uncooked cube steak should be all red, no white streaks in it.
I absolutely love a chicken fried steak but hate when someone cooks them too long. May be a CFS but they are still a steak and I want mine med rare at the most.
There is a youtube guy called Guga Foods that has experimented with tenderizing all kinds of steak every conceivable way under the sun.