I think the points raised in your OP are helpful and worth considering, and many of them are right on target (although I don't agree that sitting practice is counterproductive).
I would be concerned that the notion that "sitting practice is counterproductive" is itself counterproductive, for many of the same reasons set out in the quote you offered from Nina Van Gorkom. In particular, there's no arguing with this: "So long as one has not become a sotapanna one may deviate from the right Path, there can be wrong practice." But practice ought to be regarded as practicing the entire 8fold path, including sila, samadhi and panna as taught by the Buddha. That includes samma ditthi, right understanding.
You see where I'm going: So long as one has not become a sotapanna, one has to be aware that all those cool Abhidhamma-based views are only as good as one's own understanding at this moment, and probably a lot of them are imperfect. So for example, if a person holds the view that " lobha, dosa and moha should not or cannot be objects of mindfulness," it may merely reflect views about lobha, dosa and moha that are incomplete or flawed in some other way. Does that mean such a person is not in any way mindful of lobha, dosa or moha while engaged in sitting practice as a non-sotapanna? Or is sitting practice just that: practice, with some small seed of mindfulness of these three akusala roots even if the "sitter" doesn't realize it?
Or this: "Some people believe that vipassana can only be developed when sitting in a quiet place, but then they set rules for the practice, and thus, they will not be able to see that mindfulness too is anatta." Maybe they will, maybe they won't. The thing is, the experience of seeing that mindfulnees too is anatta is not solely an intellectual exercise.
I may be off base here, but this Abhidhammic-based approach you're describing seems to be predicated on the assumption that a person can rely on his or her intellect to develop samma ditthi, with samma ditthi being (mis)understood as constituted of correct viewpoints regarding the Dhamma. Have I completely missed the point? Maybe so. Regardless, if you look to the suttas, you'll see that the beginning of samma ditthi is the recognition: this (whatever it is) is not right view.
Also, it appears to me that the Buddha clearly taught sitting practice. So in this Abhidhammic-based approach, is it understood that the Buddha's teachings about sitting practice were intended only for ariya?
But most important, I think it's absolutely correct practice to understand that one's practice is imperfect, and to understand in particular that it's not going to do any good to sit on a cushion and try to force wisdom or peace or something to come out, like squeezing a sponge. Yet it's also correct practice to understand that there is such a thing as dhamma-chanda. So when we sit, we sit as well as we can in that moment, and that's good enough. If some folks don't want to sit at all and don't think anyone else should either, then that's where they're at, and it's as good a place as any to start practicing (again).