So much of this also depends on how you want to build your team. Polian believed in building an offense that could put up a lot of points and get a lead and pairing that with a defense that had a lot speed and could get after the quarterback. That's why when the system did fail it was often due to being too small to play against teams that can hang with them and that's why they always had a terrible run defense.
If you look at Belichick you'll see a GM who relies less on the 40 and more on big powerful guys that can pair a strong run D with a bend-but-don't-break philosophy in the passing game, so when they got to the red zone they had less space to cover and could hopefully force field goals. That's why then you saw their system fail it was often due to bigger linebackers and safeties not being able to cover more athletic players.
Both great GMs, both have their philosophies, but it doesn't make the 40 any more or less important on a macro scale just because one likes it and one doesn't.