There just have been very little contributions from anyone not named TP, TD or Manu in the last few minutes of recent games. Kawhi *might* be the exception, but I would have to check the game logs. And I'm not talking about a spot up shot, but players actually being involved in the offense. We struggled to score in the last quarter against Denver (17 pts), Clippers (19 pts) and tonight (22 pts). It gets compounded when TP, TD or Manu miss shots, which are the guys you expect the most from.
Some people will say tonight was a bad matchup for Tiago, but I actually expected him to cause the bad matchup for Miami by imposing his size. It's one of the areas where the Spurs will need to analyze how to exploit better (I'm talking overall, not just against Miami). He took only 4 shots, but he did get the ball, he just didn't really assert himself. Something else I asked a few months ago is if the Spurs are too reliant on the pick and roll? Some teams (like Miami) are really good at covering that, so you'll need some more variety. Guys like Neal, Green and Kawhi all seem to have a decent mid-range, so there should be no reason not to run a few curls for them.
Overall, I think the defense is where it needs to be. The offense has regressed, but I don't see any reason why it can't improve. Maybe it won't be at last season's level, but I don't think it needs to be either.