Is something like twin spelling polymorph outside of the original intention of the Twin Spell mechanic?

Is something like twin spelling polymorph OUTSIDE of the original intention of the twin spell mechanic? Or is that too far of an assumption?I kind of want to disallow twin-spelling spells that require concentration because it feels unfair. Am I totally off base here?No, that's reasonable

— Mike Mearls (@mikemearls) August 18, 2017

Twinned Spell intentionally works with concentration spells.

— Jeremy Crawford (@JeremyECrawford) August 18, 2017