You're very confused about the Pittsburgh trade but I'll give you time to catch up on that.
The Flames were able to make moves to bring in players like Huberdeau and Kadri because they misplayed their hand with Gaudreau and Tkachuk. They did a good job recovering from a screw up.
The Leafs didn't go out and add big names (like Huberdeau for example) after they dumped Marleau because they already had those players (Matthews, Marner, Nylander, Tavares) on the team. They didn't have to make reactionary moves like Calgary did because Marleau wasn't an impact plkayer for the team in the same vein that Gaudreau and Tkachuk were for Calgary.
Like I said, giving up a 1st to dump Marleau is bad and giving up a first to dump Monahan is bad. Your ability to understand trades is also potentially bad.
Did he has a 6 million AAV with the Leafs and a 750 AAV with SJ? Does that change his value to teams? Yes or no thats an easy question.
I'm also not certain he had a NMC with SJ the way he did with the Leafs.
If you see these two situations as parallels, I hope your day job doesn't involve heavy machinery.