I shouldn't have to explain this, but EV batteries are vehicle specific. The main reason early Nissan Leafs are junk yard fodder is because it's just not cost effective to put a brand new battery in them, and there's not enough of the cars for competition to kick in and do its thing at making the batteries cheap.
Except car batteries are cheap. If I went out today and priced a home battery system the same size as the battery in my car it would come to roughly 4x the cost of a replacement car battery through the dealer. People wildly misestimate just how fucking massive batteries in cars are.
Here's an example: Last year there was a cyclone which knocked out the power in SEQ in Australia for a couple of days. One of my friends had a V2L car, plugged it back into the house (they have some nice changeover switches, courtesy of being an electrician and from country Australia where off grid houses aren't so rare). They ran the entire house from the car for 2 days, and barely went through 10% of the car battery, that includes cooking electric, running an AC (it was January), and running a fridge.
That should also tell you something about the use of the battery here. Your car isn't going to get drained dry, these V2G initiatives only pull a trickle out of the vehicle and basically contributed fuck all to battery degradation. Unless you're running a taxi service your car is going to go from having never have its battery replaced throughout its life, to never having it's battery replaced throughout its life. In the mean time, you're paying top dollar for a home battery ignoring the perfectly good cheap battery parked next to it.
I'm glad you did explain this, it provided you an opportunity to share your misconceptions.