I love the Dark Tower books but totally agree that the latter 4 are definitely weaker. I think it is worth a read despite the time commitment but it definitely slowly gets worse towards the end with a bit of a Meh ending. My second turn of the wheel was definitely better in terms of the ending though.
Also the majority of that list you've written there are fucking great books.
Insomnia I thought was a bit over rated but not really bad.
Hearts in Atlantis and Doctor Sleep were eh.
And Fairy Tale wasnt bad but also j don't think worth the time.