Experience, in my belief, is executive leadership, familiarity with the issues, and matching the mood of the times.
Ronald Reagan, at the time of his 1980 election, would be my gold standard. He not only had first hand with the issues, dating back to 1964, but he additionally served as a major state governor. He became an experienced executive by the time he left the California governorship, and combined with his mastery of the issues, he managed to dominate the country politically in the 1980s. If an issue in the 1980s wasn't dealt with, it was frankly because Reagan didn't care about it or didn't believe in dealing with it on a federal level.
Bill Clinton comes in second after Reagan. Arkansas governor for (a combined) 12 years, fit the neoliberal 1990s, and managed to achieve a good deal. His understanding of the mood of the 1990s was invaluable. Another President might have tried to push it too far one way or the other. His centrism allowed him to ride the 1990s.
George W. Bush had considerable executive experience but had only a passing familiarity with the issues facing the United States. Consequently, Bush had a far less successful presidency than Bill Clinton. A lot of executive experience, but little familiarity with the issues. One might say had he had Reagan's grasp of major issues or Clinton's intellect, he would have avoided many of the issues, like Iraq.
Dubya fit the mood of the time -- one in which people were concerned only with the more primal drives of life or with theological fears. We know how that turned out. Dubya had good intentions in promoting a real estate boom; good intentions are not enough.
...My scale says nothing about quality aside from saying that someone who does certain things has done a few things right to be President. Joe Biden would get 16 points, yet few would want him to be elected President. He has had plenty of chances.
"Mayor of a large city" does not distinguish between being Mayor of Detroit and turning it around (should that ever happen) and being Mayor of Hempstead, New York (it really is that big -- and if you have never heard of it it is because you do not live on Long Island; it does not pass my spell-check) and doing nothing remarkable. Indeed, being mayor of Lima, Ohio (a real dump) and turning it around should matter more than being mayor of Plano, Texas. Of course, being the mayor of a small city and performing miracles might lead to the Governorship of a State or to the US Senate through the House of Representatives.
We have never elected the mayor of a giant city directly to the Presidency; our last opportunity was Rudy Giuliani.
I limited experience in the House because although having experience in both the House and Senate is richer preparation for the Presidency, being a perennial winner of a safe seat is not.
First Lady? Would Eleanore Roosevelt have been a good President? Maybe. But who better knows the intricacies of the White House -- and I don't mean where the drapery hardware sags.
