In defense of buying a used Tesla I really appreciate the idea that if your car is 'out of date' in terms of current hardware you can simply pay for an upgrade instead of being told you have to sell your car as used and buy a whole new car. When you think of how much money a lot of people invest in their cars treating it as a disposable commodity doesn't make a lot of sense economically and ecologically.
In terms of turnaround time, obviously your point is valid, but if Tesla manages to disrupt the entire paradigm of an industry in a positive way it may be a minor critique in the grand scheme of things.