As much as I usually agree with you, this time I think you misunderstood the point. It is precisely the Teals approach that allows them to work with suppliers to get the best they can for their needs, and that makes Tesla a better partner for others because Tesla 'improves the breed':
Tesla uses suppliers when they can do better from them, batteries for example:
-CATL has a growing Tesla relationship. (Elon repeats that they have no plan to replace suppliers, but to supplement them.
-Both Samsung SDI and LG are bidding on 4680 supplies and both already supply Tesla.
-Then there are the LG/IDRA cases.
- and there are a huge array of shipping and logistics relationships, some fo which seem to be very close.
and many more.
Your point about Tesla vertical integration is valid, but ignores how crucial supplier networks are to Tesla. When a supplier fails they are replaced as we have seen, but Tesla does work hard to keep suppliers efficient and successful. They must do so.