I respect the heck out of Gil Brandt, his knowledge about the game is paralleled by only a small and rare few, BUT . . . I agree with him 100%. :D
All five have contributed so much to the game, though I have yet to read, study, or listen to, anyone who did it better than Shula and Belichick.
I've never studied Lombardi but what little I have read up on him was that he was one of the first greats and that in itself is a substantial accomplishment. Walsh was a first favorite of mine to study. I still love to go though his notes and watch his clinics, but the one subject that holds him back is longevity. Landry had the longevity and holds an NFL record of 20 consecutive winning seasons, which is 5 more than his closest rival.
That leaves Shula and Belichick.
Shula is the literal undefeated champion when it comes down to winning possessing the only undefeated season in NFL history and is obviously known for his record 347 wins. His contributions also extend far beyond the field and transformed the game in many ways with his seat on the competition committee. Shula is truly great.
Belichick is the unapproachable best. To do what he has done, in terms of running an incredibly successful team from a GM and HC perspective, is for a lack of better words - mesmerizing and spectacular; especially in this day and age designed for parity. Belichick is an unrivaled strategist and nothing short of a genius in how consistently far ahead of the game he remains compared to other past and modern day coaches. Every so often he'll share brilliant pieces of information which he reveals in his press conferences; those are a gem. Belichick is by far my favorite head coach to read about and study. Belichick is the best coach in NFL history. It's a shame if you can't acknowledge that, respect him, and are missing out on a chance to witness the very best.