Not sure where your getting your 50% degradation numbers from, I have 2 years of daily use, 43k miles and only ~2% degradation.
If you're the average SV guy who 'daily drives' his Tesla 20 miles from Oakland to his lofted startup where there's 220 to full-charge before you go home, you'll get 2%. Johnny in Kentucky working the coal miles doesn't have that luxury and will certainly enter into 'deep charge' consumption. (600 cycles -> ~75%, with 2nd deriv of batt life w/r/t cycle being negative, i.e., progressively decreasing losses).
Again, not in the field professionally, but these opinions are consistent with my friends who are working at the forefront (albeit, a statistically small sample space, I openly concede !)
Your pack longevity math is grossly inaccurate.
My numbers line up with what most Tesla owner experiences. If your friends are at the forefront of the profession then I'd be a bit worried about whoever they're working for.