I don’t know if I understand your question.
First of all- the data is muddy. Not everyone who majors in mechanical engineering gets a job in mechanical engineering. A kid at Princeton could get a job at Bridgewater or DE Shaw developing complex financial instruments which pays significantly more than Boeing or GM doing mechanical engineering job. So that muddies the water.
Second- some colleges attract employers from all over the country and it doesn’t matter where you currently live- they will move you. Other colleges attract a primarily regional employer base. You can’t compare the two.
Third- I never said there is no substantial difference between schools. There are lots of differences between schools- the question is, are those differences meaningful to you, AND can you afford to pay for the increment of the more expensive option?
Is MIT “worth” the extra tuition vs. your instate option? That depends. For my kid (who did not end up in engineering, btw) the price difference for MIT was worth it. To him and to us. But it’s easy for me to say that- since we had saved for his college education since he was born. There were many private U’s with engineering schools which we would not have been willing to pay for, since the differences (to us) weren’t meaningfully better than the public U option.