I always thought the point of DNT wasn’t technical, but to make it impossible to argue either (a) that users don’t really care (many opted in), or (b) that Google et al respect user’s wishes without regulation or technical barriers (they are aware of DNT and its specific meaning and they ignore it). In other words, political maneuvering towards getting the entire industry to accept implementing that technical solution.

That’s false. I’ve had the battery in my Apple laptops and phones replaced many times. They even monitor its health and tell you when to replace it.