So getting rid of him made the Cowboys better?
Well they got rid of Walker and 4 (mostly late round) draft picks, and in exchange got 5 players and 8 (mostly early round) draft picks. In the long run football is a numbers game, and when you trade fewer late round players for more early round players your team will get better unless you suck at the draft. So getting rid of him didn’t make them better, but getting the Viking’s future certainly did.
Proof is in the pudding. Super Bowl 27, 28, & 30. They never would have got to any of them without the trade.