That only seems stupid in hindsight.
If you've just crushed all of western Europe with pzIII and pzIV, and didn't know about T-34's, why bother working too hard on pzV and pzIV?
John did leave out a major player.
Run the numbers again, and consider the effect of going from Intel 0 and gradually (or quickly, depending on the breaks) progressing to Intel 5.
Think that'll shift the numbers more to his liking.
No, but you can decide to hang a pre-existing 75mm gun off a pre-existing chassis.
Btw, for the bomber, it's more a matter of deciding to build four-engine planes instead of two-engine ones.