There is nothing special about 100% or 80%, for all current chemistries in cars, the battery ages faster the higher you charge it. There is a little bit of a step change around ~60% so keeping it below that is good for days when you can.

Genuine question. For lifepo4 I've never looked at DOD vs cycles.

Having a quick look, it seems that it's roughly linear, but slightly in favour of lower discharge?

One spec sheet I saw said 80% dod had 2500 cycles, and 50% dod had 5000 cycles, which means you get more "lifetime capacity" with a 50% dod compared to 80%?

Ok, so if you pay to unlock the higher capacity you then lose this recommended buffer?

You gain the ability to charge the full battery rarely. Useful if you do a 400 mile road trip once a month, but not useful if you do a 400 mile road trip daily and want to protect your battery life.

Imagine if you could only fill an ICE car with petrol to 3/4 full, that it would be bad to exceed that, and to bumble through life thinking this was okay.

Imagine filling up your car to 100% but only extracting ~40% of it as usable energy...

Imagine then sending the 40% through a lossy transmission network, transferring it to batteries made from cobalt mined by child slaves in the Congo, which will self-deplete if sitting unused, then telling everyone you know you're helping save the world.

So because electric cars have different externalities than gas ones we have to keep preferring gas cars?

We can change things for something with different but lesser problems. And anyway, can you 100% vouch that the gas car manufacturing apparatus has zero child labor as well?

ICE vehicles are only 30% efficient....About 70% "wasted"

Depends how telsa implemented it. If it locks out 27% of the cells entirely, then if you charge to 73%, it will charge those remaining cells to 100% each, rather than spreading it out over the whole pack, and charging each cell to 73%.

Is it possible to lock cells out using just a software lock?

They could. But it's highly unlikely. Tesla has software locked battery capacity in the past, and they did it by utilizing 100% of the cells to 73% rather than 73% of the cells to 100%.