The real lesson that people refuse to learn is that Safety Cars (as currently used) are dangerous. They cause restart wrecks in every series they are used in. F1, Indycar, NASCAR, etc. Safety cars create crashes, but unlike physical barriers, runoff and other aspects of car and track design, no one will take a serious look at why we continue to use a thing that causes so many wrecks. Insanity.
And we all know why. Safety cars bunch the field up and make a boring race exciting again. We're sacrificing the safety of our drivers for entertainment. We have the technology to create a functional system which protects track workers who have to enter the track area without trading that for risking drivers safety with restarts. We choose not to do so because we care more about "excitement" than safety.
By that logic we shouldn't have red flagged standing starts either because the start is probably the most dangerous part of the race. We have seen countless safety car restarts in F1 after SC became the norm following the Bianchi crash. How many of those have exactly created issues? All they have to do is move the safety car line to the start of the straight and any differences in closing speeds will be avoided.