"Not necessarily. Remember that West Side Story, Sweeney Todd and Gypsy were not that successful (in terms of finance and attendance) in their day. All of them closed in under two years. My Fair Lady, Best Little Whorehouse and Sound of Music all were bigger hits respectively despite being less challenging works."
Mister Matt, you are right. I look at the list below of the longest running Broadway Musicals and I have to say that, IMHO, only four of them are challenging works and the rest of them just had gimmicks that moved them along.
Cats
The Phantom of the Opera
Les Miserables
A Chorus Line
Oh! Calcutta (1976 Revival)
Beauty and the Beast
Miss Saigon
Rent
42nd Street
Grease
"Smart! And into all those exotic mystiques -- The Kama Sutra and Chinese techniques. I hear she knows more than seventy-five. Call me tomorrow if you're still alive!"