That might be the one thing I think you've said that I've found to be incredibly dumb. Diablo, and basically the entire Action RPG genre, is about loot grinding, and relies on a "Carrot on a stick" to keep the major portion of their base interested. While the gameplay itself has appeal to some, without the loot grind it would be unplayable and boring after a certain point (I mean, why grind 1000 rifts if the only experience is the gameplay or clicking a mouse on some enemies?). The gameplay and the loot work well together, but its the combined experience that makes it great... like Borderlands, if it was just a FPS, it probably would not have gotten as far as it did, despite its unique style and humor. It'd done well, but not as well.
Adding "Exclusive powerful" legendaries to a system they can clearly see has divided a good portion of the community was just a bad call. Especially if these legendaries are build changers. While most builds can work, some items undoubtedly completely change how you use the build, their viability, or increase their effectiveness greatly... like say Wand of Woh, Cloak of Garwulf, (Theres 1hand xbow that "MFDs" everything), a (Bow?) that turns Elemenal arrows into Hatred gens... so on. Some legendaries undoubtedly make certain builds far more usable and sometimes unlock completely new builds only available with that weapon (I.E the Elemental Arrow one).
While I enjoy building around what i get (I have a Physical build atm on DH cause almost everything I've gotten thats good rolled physical, I make it work), the only reason i continue to play is undoubtedly finding that legendary that starts me down a new build path (Like Cinder/Magefist). It why i sometimes keep "meh" Legendaries that don't fall into my current build, but have something like "Thunder Skill+20" because maybe I'll find a use for them if I get more thunder skill+ gear, or throw it on my MNK, or something. Finding loot that unlocks new possibilities is what these grinders are all about.
Edited_Alot
Editin: I would like to mention, If i found out there was a bow/xbow/whatever in the Seasons system that made "Bola" fire 2 more projectilces (similar to mirror ball), I'd have to play that... cause I've loved Bola builds but they're kinda weak i comparison... but a Bola build with 2 Extra projectiles coupled with the Quiver that causes them to explode instantly would make my Bola+Eminent doom build quite a bit more enjoyable, and isn't enjoyment your argument :D