No, you are not. You are bringing half the facts. If you think Gretzky's +/- on the back half of his career was an indictment of his defensive liabilities, how do you explain his otherworldly +/- in the first half? If you can't explain both, half of an answer contains no value. In that respect, you are merely ignoring the positives and focusing on the negatives. This, in my opinion, reflects an unmistakable indication of bias.
Well, guessing about what might have been and what actually happened reflects a significant incompatibility. Gretzky was +45 in those two seasons, and Orr was +8. That's a fact. The +48 number is fiction. Also, through their age 30 seasons, Gretzky was +606 and Orr was +574. That's equally a fact.
When delving into the realm of fantasy, I'm sure Gretzky's +/- would have been higher if he were provided the advantage of Orr's circumstance. If the mid-80s Oilers were beating up on a plethora of expansion teams, I'm willing to bet Gretzky's per game rates for +/- would be higher. Due to the nature of deployment for defensemen, Orr was likely padding his +/- by logging additional ice time against weaker players. I'd also be very interested in seeing Orr's per game rates with all those expansion teams removed. It's likely somewhat less flattering.
Gretzky and Orr are very comparable in +/- rates at their peak. That said, does anyone genuinely believe Gretzky is in the same universe defensively when compared to Orr? That alone should indicate +/- is an exceedingly limited statistic when considering defensive acumen. In point of fact, it's effectively useless.