Yeah that in no way justifies the trade. In fact, if you were to ask me, it made it worse, but we won't go there.
What the trade did for L.A. or all of California or Mexico or Yugoslavia or whoever has no barring on how dumb it was for Edmonton. The argument that they won a Cup 2 years later still doesn't justify it either. They were fortunate to still have other pieces in place (Messier, Kurri, Simpson, Ranford coming up huge of course), but that compared to what they could have been is nothing. I think it's mostly those who weren't around at the time who say that stuff.
I've heard many say that the oilers would have won anywhere from 2-5 more Cups on top of that last one had they kept Gretzky. I argue that 1-2 is more realistic, but that's still pretty big regardless, and the overall big picture of what trading the best player in the league and to a guy who to most is the best player of all-time did to not only a franchise but an entire city has to be realized. They were completely hosed, and what the trade was all about ($$) has to be realized as well.