At the time, the Murphy-Engblom trade wasn't considered to be a bad deal for the Kings. Most observers felt it was two teams addressing a need: Washington needed offence, Los Angeles needed defence. Murphy was obviously talented offensively, but prone to defensive lapses. Engblom didn't score much, but was a excellent stay-at-home defenceman. It looked like both teams would benefit.
There's a LA-Bos game on YT that took place shortly after the trade, and the Kings announcers are pumping up Engblom about how they finally have their defensive centrepiece on the team who can play 30 minutes a night and be their rock on the blue line. Things didn't work out that way. Engblom suffered an eye injury late in the previous season when he got hit with a puck, and indications seem to be that he was never the same player after that.
The book on Los Angeles in the 80s was: great offence, terrible defence. It figures that the one time they tried sacrificing offence for defence. it backfired.