Every battery you put in an EV becomes a battery you can use to balance the grid when the EV is scrapped and the battery still has 80% of its capacity left.
80% capacity does not mean 80% of life span remaining. Degradation is not linear [1] [2], a battery that's gone through enough cycles to drop down to 80% of its capacity is very close to the end of its life just a few hundred more cycles before failure. That would drive up the costs of labor as these recycled batteries would have to be replaced once a year or even more frequently.
Recycled EV batteries are popular in DIY communities because labor is free, and if they fail you still have the grid to fall back on. That's no the same case for grid operators. New LFP batteries have better economics than used EV batteries for grid storage, especially since they are both cheaper per watt hour and they have over twice the life span of most lithium-nickel-cobalt batteries used in EVs.
So you're saying your point about every battery going into an EV is completely irrelevant because grid batteries will most likely use different chemistries than EV batteries? That's fine too.
