If you can convince yourself that Phil Kessel and Carl Hagelin were the catalysts for a Pittsburgh team that had Crosby, Malkin, Letang, and had already won one Stanley Cup and been to another Cup Finals before they got there, you can probably convince yourself of anything. But, if you do use your list of catalysts, then you have to consider how LA got Mike Richards. It was trading Brayden Schenn who was a top-5 pick who still had a lot of promise.
Really though, you need to re-consider what tanking actually is. Detroit and Vancouver do not fit the bill at all. Both teams propped themselves up into mediocrity by signing over-priced UFAs in order to try and remain competitive and more importantly, they haven’t seen a single draft pick in the top-3 or higher. Vancouver has hit Hughes and Pettersson in the later parts of the top-10, but Detroit still hasn’t drafted a single can’t miss franchise player. If you tank right for many years, you will get at least one franchise player pretty quickly.
Until those two came over Pittsburgh was going nowhere in the playoff. They were irrelevant for a good 5 years until, well, Hagelin and Kessel were traded to Pitts.
Vancouver did hit on Pettersson and Hughes, but they have been rebuilding since 2013. Buffalo has not had a positive season despite drafting Dahlin (1), Eichel (2), Reinhart (2), Mittelstadt (8) and many other mid to late first round pick.
The biggest need these teams had at the time were leadership. Just like any other jobs, when you’re a kid and starting your career, you have to have somebody to look up to and the better that person is at said job, the better you will become the long run (granted you are talented at what you do). The amount of players that can become that “guy” where teammates leech upon for knowledge, work ethic, techniques without learning it from someone else could probably be counted on a single hand (these guys tend to be generational talents - Crosby, McDavid, Kane, Doughty, Weber come to mind)
Having those players in your team goes beyond the play on the ice. Younger guys leech off these guys in all aspect of the game - from inside to outside the rink and it helps them become better hockey player in the long run.
This is (in my opinion) why some veteran will never get traded unless they request a trade. The Sedins, Chara, Weber/Price in Montreal is a couple examples. The value these guys bring in leadership for your future core is so much more valuable than what their market value would be to a contender.