You forgot about Teddy Roosevelt succeeding McKinley. Cooledge succeeding Harding. Truman succeeding Roosevelt, and Nixon succeeding Eisenhower (in 1968. He would have won in 1960 except for Chicago fraud).
VP is the best office from which to become President. Governor is the second best.
. . . none of whom were elected president while sitting as VP.VP is the best office from which to become President. Governor is the second best.
VP is the only office from which to become president without being elected president. So in that sense, this is true. But VP is a better office from which to win the nomination of your party than it is to be elected POTUS in your own right. If your sitting POTUS isn’t more popular than most two term presidents are in their second term, you don’t win.Anyone running to succeed a sitting POTUS of their own party has that issue. A sitting VP has it in spades.
I agree that governor is an excellent credential for a presidential candidate. Because, IMHO, governor is an executive position, like president (or mayor, which is inferior to governor). In fact the only senator or VP to defeat a governor in a presidential race was Harding, who defeated the governor of his own state (Ohio) in 1920. That Democrat governor had a terrible headwind trying to succeed Wilson, also a Democrat, who was unpopular at the end of his second term.
And no senator has ever beaten a sitting president. When you look at the Democrat candidate field, I think you don’t see any prominent governor in the mix. Hickenlooper, I think - but "Hickenlooper who?”
Lots of things have happened for the first time, of course . . .