A low grade plug may wear out from repeated use, and loose tension, but to be UL listed it must be able to carry the rated current.
The problem with blaming the plug for not being able to handle EV charging is that the leaf can only draw a little over 1/2 the rated current (55%) of the circuit capacity. Code states that "continuous" load must be less than 80%. So for a 50 amp plug, it should be loaded no more than 40 amps. The Leaf is 27.5 amps.
So blaming the outlet for not being able to carry 55% of it rated capacity means either knock-off outlets that can't meet UL listings were used, or far more likely that the connection between the inlet wire and the outlet was a poor connection.
By your reasoning, a std 15 or 20 amp outlet would fail when a toaster is plugged in.
Better grade outlets can stand more plugging and un plugging before they loose tension, but all grades should be able to take the rated current, 50 amps for under 2 hrs and 40 amps continuous.
I put this squarely on the person who installed the outlet. Bad workmanship.
Another proof that it is poor workmanship is: of the two current carrying wires, only one suffered overheating, but both carry the exact same current.