I don't think we are - discussing more hypotheticals isn't helping
What would help me is understanding Ian's logic below (post
#140)
I don't understand how the ref can accept advantage has been gained but then go back to the original infringement.
And to be clear again with my understanding (happy to have it improved!) if it was knocked-on into in-goal, I agree it is a scrum restart but not because of Law 12 (which covers the original infringement) but because of Law 22.7(b) i.e. we are not restarting from an infringement, we are restarting from a touch down (which is what 22.7 covers).
The fact that 22.7 (Restarting from a touch-down) has a special case for if the ball went into in-goal from a knock-on in the FoP, but no special case for a knock-on in-goal is a very significant and (it seems to me) intentional difference.
I think there is no way of getting to 22.7(b) without having played advantage after the original infringement; so that tells me advantage can be gained in this scenario (attacking knock-on into in-goal) by the defender grounding the ball. I therefore think we can call advantage gained in the scenario of defender grounding after attacking knock-on in-goal.