It's an amazing accomplishment, but the fact most of those SB wins, there was a controversial reason why they won that year, will follow him forever.
Though in the future people will just see the SB appearances, and wins, the information of things being done to give his team an advantage will always be there also, and will hurt his legacy.
Right or wrong to put so much stock in it, but Shula did it the right way, and Belichick always tried to find an underhanded way to give his team an advantage. Not a coincidence that when he behaved himself, and did nothing deceitful, they rarely did not reach a SB or win one.