I can agree with your assessment of his game right now, but your conclusion is ridiculous.
It's very clear the Habs are in a phase of their rebuild where they can afford to be patient. They don't need to move on from anyone. If Buffalo moved on from 23 year old Tage Thompson, it would have been an incredible mistake. Of course it's unlikely Dach ends up as good of a player, but even that slim chance is worth taking because the Habs have nothing to gain from not rolling that dice. The trade is done, the gamble has been made already. They need to see it through.
My main problem with Dach is that he is playing like a guy afraid of getting injured again. He's not banging along the boards like a guy his size should be. His offensive calling cards are silky hands and good vision, and I feel like in order to make the most of those skills, he needs to become a dominant, physical puck protector and board player, à la Joe Thornton.
Let's hope he regains that physical edge as he becomes more confident that his body can take a hit.