I think it should have been done for two reasons.
1. The chance to gain assets for the next generation. Who knows what you get from Toronto, but it would have been alot for Doughty, maybe you end up with a guy like Nylander, or a couple of 1st round picks. That is certainly better than having Doughty age a half decade and have 0 playoff series wins to show for it and have a potential franchise defenseman traded because Doughty was blocking a quick ascension.
2. Doughty wanted nothing to do with the mentorship role in a rebuild that you suggested. Look at this quotes to the media "frustrated as hell", "sick of losing" in what was the very early stages of what would have been a traditional rebuild, as I like to call it. And of course right after those comments were made the Kings began going down this reload path. Doughty going to the media was smart for him, it created a fork in the road that was going to result on him playing on a playoff caliber team, either through trade or the Kings going to this reload strategy.
And I don't personally blame DD, I probably would have done the same thing in his shoes, I wouldn't want to have the last years of my prime spent in a 3-5 year rebuild. I blame Blake for not making the tough, but necessary decision to commit to a good rebuild.
I don't think he can trade PLD at this point, it would result in massive salary retention, at some point you have to figure AEG is going to say "ENOUGH" to paying people to not play for and not coach the Kings.
Not all Blake's fault...but.
Richards
Phaneuf
Greene
Stevens
Cal P/ Provorov