The boys of Twenty One Pilots have mental illnesses, too. They cope with their illnesses by writing music about it, just like you cope by writing poetry. Not liking them because their lyrics are corny is a good reason to not like their music, but you can't say that they make mental illness seem trendy and cool and mysterious. Their whole goal in writing & making music is to encourage others who struggle as well and remind them that they aren't alone. Not romanticize it.