If you are going to change up the core, you still need to get some core player back though. Most of the Nylander trades have been trading him for non-core players, or to open up money for non-core players. That is not what any of those teams did. Washington rode Green and Semin until they were no longer "core" caliber before replacing them with those other guys, and the Avalanche traded away their core players when they were still a rebuilding team; not in the middle of their competitive window. By that extension, the Leafs already moved on from Kessel, Phaneuf, JvR, Bozak, Kadri, etc. and unfortunately the only core player worth keeping from before our rebuild was Rielly.