Interesting discussion, as I've always believed the opposite to be true - mileage doesn't matter much and the biggest determining factor of battery health is the one variable we have no control over - the age of the battery pack. It's one consideration when choosing between a newer but lower trim EV and a fully loaded older trim EV - the older one is more likely to have more degradation, all other things being equal.
Obviously, high pack temperatures, frequent overcharging, habitually driving the EV past the low battery warnings, leaving the pack at 100% charge for extended period, and other such battery "abuse" are super important. But, when buying a used EV, it's almost impossible to tell which battery packs were abused and which were not...
Anecdotally, when I was shopping for a Leaf, I found the battery health seemed to have little to do with mileage within the same model year. I think it's fair to say that location is the biggest factor - the hotter the climate, the worse condition the pack will be in. I ended up purchasing a higher mileage Leaf with a battery pack in excellent condition (PNW car) because I think the OPs perception is common - that mileage is of paramount importance for EVs. I don't buy that argument though, but I'm glad that others do as it got me a nice discount
Vancouver, CA owner of a 2013 Ocean Blue SV + QC, purchased 01/2017 in WA
Zencar 12/20/24/30A L1/L2 portable EVSE
1-1/4" Curt #11396 hitch
After market, DIY LED DRLs
LeafSpy Pro + Konnwei KW902 ELM327 BT OBDII dongle
Loving my first BEV