At this point, signing RJ is good for the Spurs. He was certainly the best player available to the Spurs. Once they get the signing out of the way, RJ and Pop have work to do.
I think everybody was disappointed in RJ's performance last season. I was. I bet you were. I think the Spurs were. And, I'd bet heavy money that RJ was. The across the board frustration and disappointment is why I wouldn't have been at all surprised if either the Spurs or RJ had decided to sever ties. Honestly, I'm a bit shocked that this is happening. My guess was that he would be a trade chip all next season. But then he opted out. Then I thought he'd be more of a sign and trade piece. That doesn't seem to be the case. I really didn't expect the two parties to want to commit to a long-term deal given what transpired last season.
Now, with a season in the Spurs system under his belt, will he be able to get comfortable? He better be. I'm not sure what the terms of the deal are, but it has to be multiple years (at least 3) at 8-10 per. For that kind of investment, he has to be a big step toward making the team a serious contender. I think the onus is squarely on RJ and Pop to "figure it out". This is a new deal that they have each voluntarily entered. They both know what they are getting into.
I don't really know what I mean by "figure it out" in a game-to-game technical sense. But, they need to figure out a way to make him fit with the system. He has to be effective on defense. He needs to be a threat on offense. And he needs to be able to play the 4. RJ and Pop have their work cut out for them.