While I'm not a fan of the policy, it does make sense to me from Tesla's perspective. It only takes one mistake in an inspection to miss something, and imagine all the bad press of "Tesla bursts into flames at supercharging station", if they missed something in any one of these refurbishing salvage inspections. DC fast charging is the highest stress the batteries experience, by far, as well as the aspect most unambiguously reflecting negatively on Tesla if it does go wrong (they can't argue that it was a noncompliant 3rd party charger, or that the driver was driving erratically or inattentively, or anything like that like they could with most other potential Tesla mishaps.)
It makes sense to argue that if it's superficial damage that doesn't affect the battery or wiring then they should allow it, but, again, I suspect the blanket policy (applying to all salvage cars, no exceptions) does make sense in an effort to eliminate any potential judgement calls (and thus potential judgment errors) on the part of the service technicians.
Regarding the discussion of qualifications, I don't claim to be an expert in Tesla's electrical systems, but I have worked with electronics for over a decade, and taken some classes involving dealing with these sorts of high voltage/high current systems.