A car's assumed lifecycle is around 15-20 years. Practical suburban EVs have been around for around half that, practical ICE-replacement EVs for about a third. Consequentially, EVs have not yet arrived in the econo-shitbox segment of the used car market, and it will still take some time for them to get there - this is simply a lifecycle question and not a "new product introduction question" (which most of the press gets wrong for obvious incentives).
That being said, there's an argument that even basic EVs are often much more pleasant to drive and less hassle overall, which could be a reason for them to command a sustained premium on the used market.
How are EV's going to get to econobox/shitbox levels when the batteries go bad in less than half the time you mentioned and it costs ~£5000 for a new one?