Arnolds marriage to Maria was on the surface, on paper, the perfect one. Maria looked good(?). Political power et cetera. Had four kids, two males where both seems to be a little dandy.
Mildred supposedly was in a spur of the moment, where his impulses drove him.
Just look at what produced the "best" offspring, this kid beats all the Kennedys with arms tied behind the back.
If Arnold was a ancient king he would make Joseph his successor obviously.