Not saying that I agree with the pictures below, just a "re-tweet"
https://i2.wp.com/www.footballxos.co...00%2C222&ssl=1
https://i1.wp.com/www.footballxos.co...00%2C222&ssl=1
The basic assumption is that the DE has longer to travel to the QB.
But like you say. The DE is not compelled to travel that path if he stunts or the DC Zone Blitzes with people up the Middle.
Also, the assumption is that the Defense is going to use 330-lb Defensive Tackles versus the Air Raid. Seems they put DE's across the Line or OLBs. So the DE is actually much closer than the magic little triangle.
There needs to be an implicit run-threat, too. That's the only reason the DL would balance across the width of OL or even match physical sizes with the OL. If the OL really sucks, just close ranks and jail break up the middle in limited blitzes.
I just watch football, ask me about soccer for more educated opinions.