Much of the time, that's true, but there's no reason to doubt it in this case. There's a lot of talent in LA's pipeline, but none of it looks likely (if even able) to replace Kopitar and Doughty, at least in the next 5 years. Those two are necessary for stability so that the prospects are brought up the right way. Trading them would set the team back years and risk a situation like Edmonton was recently in, where the young players were forced to develop while carrying the burden of winning and the team spun its tires year after year.
Kopitar would help any team to become a contender. He just isn't enough, by himself, to make every team a contender.