for a bunch of reasons. first off because that's a boring rehash of otl, and that's no fun.
also my mind works funny. i tend to focus on the unsexy details that don't show up on paper. note how that table never included the power of the ammo, only if it was available.
as long as a piece of kit can do the job it has been assigned then factors like cost, availability, and reliability are more important to me.
not necessarily, aiui the .50 cal guns worked just fine on any plane other than the 4 engine heavy bombers
here's a video on the p47 and it's armament. of note is a chart stating at 16:40 showing the comparative mass of firepower in grams per second. the 50 cal arrangements are extremely competitive in this category. later in the video he presents evidence that you can often score dirty hits with a 50 cal armament where a 20mm gun will give you clean miss.
but yeah for early war a .50 cal will do just fine