I'm not that old, but the majority of our Secretaries of Defense have been politicians or essentially time serving door steps. Gates, who I didn't necessarily agree with, was probably the only other competent SecDef within my life. Mattis... This isn't a job. Or the capstone to a career. This is his life. He's dedicated to the defense of this country in ways that virtually no other SecDef or equivalent since the War of 1812 has ever reached. Or probably will for a long time. We have absolutely no clue how lucky we are.
As I've stated repeatedly. I don't like Trump. There are times however when I believe all the negative costs of his election will be worth every last dime, literal or metaphorical, just for having Mattis at the head of our military.