Few times in sports can I remember seeing a situation as complex as this where you have a player fully deserving of every penny he can get, but one who is such an overwhelming injury risk on literally every play. That risk will only increase with age and more wear and tear. I slightly disagree that with your point when it comes to the timing of the contract as it relates to injury though. At the time he received the new deal there was concern obviously about the back, since that cost him his final season in college, but not really anything else, as he hasn't missed a single game or practice yet as a pro to that point. So I don't think the team felt it was that much of a concern at the time. With that said, however, he did choose to sign on his own volition.
It's so tough to manage these kinds of things and I don't envy the financial guys at all. As Gilbert Arenas said, a player is getting paid for past production when a team decides to reward said player with a huge contract. He would know because his deal is considered one of the worst of all-time. Lol He hasn't been in the NBA for years now and is still getting paid with more on the way (until 2018 or so). Unfortunately for football players, basketball contracts are fully guaranteed. But yeah, Gronk deserves the money and any new deal should help the salary cap in theory.