He was overpaid . . . like a lot of players.
You're dismissing that way to easily. Shaun Alexander the previous season signed a deal that was worth less total and only $2 million more guaranteed. After he had won the NFL MVP.
Relatively speaking, if you look at what the player signed for compared to the average salary of his position Bush might have been one of the most overpaid players in the 12 years.
And, yes, he was an integral part of the Super Bowl Championship year.
Rank that years roster 1-53, based on how unlikely the team still wins the title that year if the player got hurt week 1 for whole season eg Drew is 1.
Now tell me where are you putting Bush on that list?