FWIW, many commercial EVSEs are fed with 208-v nominal power. 208v*30A=6240w. 30A is a fairly typical max current on them as well, although newer ones may be 32A.
Depending on how hard the vehicle is run, how long the trip is, and whether they set a departure time, would all play a part in how hot the battery pack got. Once it's hot, it can take a long time to cool off. Higher demand means a hotter battery. So a high speed run done without setting a departure time, then sitting in a hot parking lot and trying to charge, especially with a CCS unit, could be the worst of possible conditions and affect the battery longevity probably the highest.
Batteries are often rated at how many charge cycles they can support and, given the same range, a smaller battery pack will need more recharge cycles than a larger one, and that can play a factor in it as well. A charge cycle is defined by a 0-100%, so one of those is approximately equivalent to 10 recharges from 90-100%.