800 cycles is about what a typical mobile phone sees in two years, after which most are seeing some moderate degradation (70% of new condition is fairly typical) but are still quite usable. And in fact a car spends much more of its time being recharged well before reaching full discharge (where consumer electronics runs dead a lot), so it would be expected to do somewhat better.
It's not really a problem, basically.
[1] Though we're seeing an increasing number of vehicles delivered with LiFePO4 cells. This chemistry has somewhat lower energy density and higher internal resistance, but has the advantage of an estimaged hundreds of thousands of cycles lifetime. Those will never wear out until long after the mechanical parts are dust.
An EV battery loses capacity faster in the beginning, slower later on. The falloff is perfectly predictable and easily estimated. You can check the health of a battery pack with a free app and a $10 OBD2 reader when buying one.
Yes, the maximum range will be lower than it was new, but it's up to the buyer if that is something that bothers them.
Compare this to the process of buying an old car. There's no way to know what kind of crap oil the previous owner has put in. You can't tell what shape the engine is in without actually opening it. The gearbox might just decide to break one day, the clutch might be on its last legs and the pistons might just come up for air some sunny summer day to enjoy the weather.
The only way to check for faults is relying on educated guesses (bring a friend who knows the specific type of car or take it to a shop for evaluation).
The difference between an ICE and EV is that ICE needs money frequently (oil changes, belts and chains and whatever wear down), an EV has That One Big Repair coming up at some point. And the price of batteries is steadily going down.
For example you can get a 3rd party battery for a Nissan Leaf _today_ that's 30% larger than the one that was in it originally. Just think what we can do in 2030.
That happened to a friend of mine, who was quoted around 50k NOK (~6k USD) of a car he bought used for twice that. Fortunately for him, it turned out there was one week left of the 5-year "new car" warranty so he didn't have to pay after all, but that was sheer luck.
https://insideevs.com/news/405885/tesla-model-s-battery-afte...
https://electrek.co/2020/06/06/tesla-battery-degradation-rep...
https://www.findmyelectric.com/blog/how-long-does-a-tesla-ba...
I ask because the lifespan of current batteries seems to be around 8 years (going by manufacturers' warranties), and the battery pack amounts to approximately 30% of the price of the car. So people buying an used electric car will likely face a large maintenance cost after a while.