So…
Sam has to drink demon's blood to be strong enough to become Lucifer's vessel
Jack has to eat angels' heart and performs rituals to become Chuck's [omitted]
And Dean?
Dean just has to say 'yes' to become Michael's vessel.
His inherent power (maybe his soul's power?) is... impressive.
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Sure, it could be seen as a Michael's characteristic, given what happens with John in the past and Adam. But:
• Supernatural took the time showing the best and most-hearted angel can do this
to a human he's angry at some episodes ago.
• There was the whole warning in 5x03 about the fate of archangel vessels, Cas showing him Raphael's abandoned vessel and going
• Michael had a good reason to be careful with John in 5x13 (John had to live and follow the script Heaven wrote for him). In 15x08, Adam points out they have an agreement because they "only had each other" after falling in the Cage. The situations with John and Adam are presented as the exception.
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Return to Dean as the Sword
Dean fights for the control of his body against a ruthless archangel and the best Alternate!Michael can do is… [check notes] trapping him in a simulation? He doesn't tear his mind apart? He doesn't destroy his soul to have the vessel only for himself?
(Jimmy is dead and Cas still uses his body as a vessel; despite Donnie's state, Raphael uses him as a vessel again ; the human has to say yes only once and death can't free them.)
And later Dean is the one who manages to trap the archangel in his own mind? And said archangel'd rather flee from his True Vessel and lose the power he had with Dean (Dean who was unconscious at the time) than risking being trapped again?
