I didn’t think I made such a distinction, but perhaps it came across that way. I was just using emptiness in general.
This is precisely my argument for being pragmatic with altruism - Nile river is samsara, dukkha, insubstantial and empty yet source of suffering. Nibbāna, in contrast, is the absence of the river, absence of samsara, absence of suffering. All kamma is ultimately dukkha, and the teacher explains the way to cessation of kamma.
A truth proposition doesn’t have to be substantial to be true. None of teacher’s arguments have a substantial soul, yet they are true. 
Otherwise, we can run into some weird paradox statements. For example: If insubstialness of things as a truth proposition, being insubstantial itself, should be let go, it’ll result in the proposition that things do have a substantial nature. Hallelujah, Moses was right! 
Then there’s an eternal soul, things are permanent, evil deeds can result in good fruits, one should cultivate a heart of hatred for nibbāna, so on and forth.
Thanks for entertaining my query, I guess we’re just not going to see eye to eye on this. I would enjoy discussing this elsewhere if you cared, we’re probably stealing the topic with this here.