If you think Tesla is making a mistake here, let's watch how it plays out for those manufacturers who think it's a good idea.
I go back and forth on VTG. Ford is either going to have to limit how often the trucks can be used for this purpose (walking back on their marketing), or they will face a massive warranty cost for battery degradation.
IMO the real value of VTG would be for utility companies to be able use them for demand response. The savings are there for utilities, but they are rarely agile enough to take advantage of something like this. They would need to seriously subsidize the utility bills for customers who signed up for this.