The higher win% can also be attributed to the fact that Outlaw was more often on the floor during the 4th quarter than Batum was. We were one of the best 4th quarter teams in the league this year, but I wouldn't necessarily attribute that fact to Outlaw's presence so much as our depth and Roy's late-game transcendence.
Chicken and egg situation here, are we as good a 4th quarter team because Outlaw was in in the 4th or was Outlaw that good because he was there in the 4th...
The reality of the situation is that Outlaw mostly played with the starters in the 4th and we were a good 4th quarter team... this reflects on both sides.
What Nate did is really a smart thing - Outlaw is really effective as a scorer - but his value as a scorer is especially high when he can take these impossible "shit they broke our play let's throw it to Travis" situations - so Nate plays him with the starting unit only at the end of the game when the opposing team has made their adjustment to stop whatever else Portland was doing - while going to the structured offense through LMA at the start of the game.
Collinearity does not equate to causation, and the argument is relevant on both sides (re: win% and +/-). My argument for Batum would simply be based on that which I see, not based on statistics that may or may not support my position.
The funny thing is that Outlaw's stats are better individually (PER) and in team wins (win%) - Batum is a more consistent player (he will not dominate a team and he is not going to kill you with stupid mistakes) and he does not need to score to be effective - these are his advantages.
Travis can win you a game and can force the other team to pay attention to another scorer to make Roy's job easier - he is more valuable at this stage at the end of close games.
I have no doubts in my mind that overall Batum is a better defensive player - especially when it comes to consistency. I suspect that if you need to have one defensive possession you need to stop - Travis will be just as effective as Batum or even more so - but he does not play defense as consistently and will hurt you with some dumb plays.
I hate it when people resort to "my eyes tell me" and "it's correlation without causation". I am more than happy to acknowledge problems with statistics and the fact that they are not the end-all of everything - and I am more than happy to require an eye test in addition to statistics - but the fact of the matter is that we have a pretty capable coaching staff which seems to go with what the statistics tell you. At this point it comes down to "the statistics do not agree with my position - so my eyes are better than the coaching staff".
This coaching staff is very successful with these guys and the statistics do not support your position. When these things align - no offense, I am going with the professional eyes and the stats over the "correlation without causation" catch-phrase.