I'm thinking that the thumb over grip works well with the AR mostly because of two thing: low recoil, . . . and high sight plane.
Trying to do that with a Browning Automatic Rifle (GI or Civilian) puts your thumb in the sight plane and does not give you the control you need for the recoil.
Same for M1Garand and M14, . . . IMHO.
But I also think it is quite useful in a CQB situation where fast acquisition of the target is necessary, . . . and one is practically doing all point shooting.
I'm still the guy who grabs a hasty sling on my AR, though, if I'm "out and about", . . . up close I have the hand wrapped around the base of my Vietnam triangular handguard, . . . right at the chamber end.
Just my $.02
May God bless,
Dwight