The Tin Man missing his heart, consisting of hundreds different pieces, all of them hollow, empty perfectly describe Dean’s struggles throughout his MoC arc. The feeling of hollowness, being (an) empty (vessel) and devastated, at the end of his strength determined so much when Dean took on the mark. And it provided a feeling of calm and belonging. Basically it filled the ache and gaping hole Dean felt in his heart. And that is why it was so dangerous. It made Dean feel better. For the first time in quite possibly forever.
The Scarecrow missing his brains and the tin man missing his heart. Crowley labeling the Winchesters here has never been more fitting. Sam, who is possessed by an angel, has his mind invaded and sometimes scrubbed clean and experiencing his body later being used by Gadreel to kill Kevin fits the bill of the scarecrow pretty well. Especially in relation also to 10x05 “Fan Fiction” in which Calliope uses the scarecrow to kill too. And yes, in that regard it makes perfect sense that both Sams in that episode contribute to killing Calliope/the scarecrow. With that action one could say Sam cut himself free from being the scarecrow.
But the Scarecrow didn’t stop existing, it just started to live on in Dean, who is still the tin man, too. Especially in S11 when Amara was pulling his strings like Calliope was pulling those of the scarecrow in the play. To this day Dean may have shed the scarecrow, but the tin man’s heart - though beating strong in the center of his being (because it was never gone, the tin man in Oz after all also in the end finds out he had a heart all along) still hasn’t truly healed and maybe it never truly can or will, and so far it doesn’t look like S12 will end in providing at least some possibility for Dean to be able to work through everything he endured in the past three years and put himself back together. But one can hope for the next season, right? ;)