@jwildeboer empirically my 5 year old Kia e-Niro shows essentially no visible degradation at all. Last summer I was still getting 280-300 miles range on mixed driving scenarios, which is over the official stated 270 mile range at new :-)
The only common cars where you had significant degradation were first generation nissan leaf which lacked any battery thermal management and a small battery to begin with. I wouldn't hesitate to buy another secondhand EV - much less to worry about than a secondhand ICE with countless moving parts to go wrong.