I've heard this opinion expressed before, but I'm not sure. In 1992-93 (as in every season from about 1981 to 1995, excepting 1990-91), the Kings' Achilles' Heel was team defence. They were not weak at offence at all. Indeed, after trading Coffey, the team scored 33 times in a six-game series vs. Calgary. They had young Rob Blake and Alex Zhitnik on defence, too. So, I'm not sure Coffey wasn't sort of expendable. Of course, who knows how he would have impacted a series like the Final against Montreal.
With those kinds of trades, the problem maybe wasn't so much that they traded Coffey, but rather what they got for him. I have no idea why Kings' management would have thought getting Carson back, in exchange for Coffey, was decent trade value.
When Coffey arrived in LA his back was bad. He would continue stuff his feet into skates vastly too small, shoe size 9/9-1/2 skate 6-1/2 to 6-3/4, and over time it caused back problems. Discounting the game in Edmonton the day of the trade, the Kings played 20 more regular season games, Coffey played in 10 that season. In 92-93 Coffey was experimenting with somewhat larger skates, 7's and 8's and was feeling better. When he arrived in Detroit the first thing they did was demand he wear larger skates, 9-9-1/4 to take pressure off his back, which Coffey himself stated it prolonged his career.
In 92-93 the Kings due to Gretzky's absence, though they played well, they lacked scoring up the middle. Couple that with Millen who also couldn't stay healthy, the Kings basically had massive questions at center. Plus another winger whom the Kings relied on to score was Sandstrom and he was always hurt.
With Blake, Sydor and Zhitnik they for sure had the ability to score from the back line, and McSorley was have an out of his mind year on defense as well. But the Kings needed center/forward help and by the All-Star break McNalls world was starting to crumble around him. That trade saved him money for sure, but who knows if it was the reason, or part of the reason. Or was it simply a deal where you got a little bit weaker in a strong position by trading for strength in a currently weak position. Or was it McNall strictly living up to his pledge to trade for Carson as he promised.
IMO the deal benefited the Kings short term as Carson came in and did what they needed him to do and take a load off Gretzky and was a big cog in the Calgary series. I don't think the Kings go as far with Coffey, and not because he wasn't a dynamite player. But with Gretzky, Millen and Conacher, Johnny Mac and Lang at center, I just don't see those 5 carrying the Kings to the Finals. And with Robitaille who was coming off a career year in 92-93, he couldn't check his hat in the playoffs.
And any deal in that era always has to be looked at with the mindset. Does this deal save McNall money?