I think with. Kawhi is a phenomenal player, but to expect him to be playing at his MVP level of last season (which let's face it, is the only way Spurs can even get to the second round) is too much this late in the season. And there's also going to be a lot of awkwardness in trying to fit Kawhi back in. The offense is atrocious and Kawhi should help but I don't think it's going to be seamless and the Spurs don't have enough time to be firing on all cylinders come playoff time. Had Kawhi returned in January the Spurs would have had a much better chance integrating him.
An 80% Kawhi isn't going to beat Harden and CP3. Yes, Harden was last year but CP3 historically owns the Spurs and the Rockets got significantly better over the summer while the Spurs got significantly worse.