Why would you reuse batteries in cars? If it has lost enough capacity to be taken out and replaced then you don't put it in again. You put it somewhere where the lowered energy density doesn't matter. Portable battery packs, off-grid cabins, peak shaving setups, hybrid conversions etc. Reusing battery cells is far easier than repairing a transmission.

No, batteries don't cost more than a car. A 30 kWh leaf battery can be had for less than 5k. You'd likely spend more than that in maintenance on an ICE over 10 years.

You say any diesel is 99% likely to make 500k miles. First of all, that is BS. Second of all, plenty of taxi companies have driven EVs for 1m+ miles. There is a reason why they are the car of choice for taxi services.

As for car emissions being a relatively small source of emissions - sure. But it's also one of the easiest sources of emissions to get rid of. The technology is already here. I think a more important often overlooked point is the effect smart charging systems and recycled batteries have on allowing us to build a more dynamic grid capable of being powered by cheap unreliable renewables. Renewables don't work well enough without storage - old electric cars get turned into cheap grid storage, which makes a full renewable transition easier.