I have no problem with both Tom and Gronky leaving, and I understand both had issues playing for BB again, but for different reasons.
For Gronk I think the problem is more about the rigors, the mental stress, I think he feels he's always been underpaid even though he got that big money (at the time) upfront and he knows that, but considering the way all his injuries have been mismanaged at times and the fact he always put his body in the line of fire and gave 100%, I think he feels underappreciated.
For Tom, I think he was tired about saving BB's the GM azz every year and not getting some return or some help, recognition, money or anything in between. Seriously, BB has been fielding putrid offenses since the draft of Gronk and Hernandez and last year it was a shame.
Now not only his drafts are terrible but there's a cap aspect to it as well. The Pats found themselves in this offseason in cap hell with no QB signed. And now we are in this situation because they didn't have money to pay Brady (I still think money was not his main goal) and to sign receivers for him to throw the ball and that's the main reason he left.
Teams around the league are paying more money to their QB's and still able to sign good players.
There are many ways to build winning teams, spending in starters and throwing the depth on the toilet, the opposite of that, and a middle ground. BB has always choosen to spread the money all over the roster and you can't deny it worked out but you can't really have depth if you don't draft well. There's not enough money to pay for good 53 players if you don't have a bunch of them in rookie contracts. You have to have some organic depth created through draft. And that's where I think the Pats lost some track in the past couple of years resulting in last year roster and this years (pre-draft of course) roster that is now considered a bottom 5 in terms of talent.
I don't have any confidence in BB doing a great rebuild, he has many picks so he will hit a few of them of course but it is my opinion for a long time he should only coach and someone else should be the GM, it could be Caserio but with 100% autonomy, right now he's just a intern senior level.