> Ok, where is today's Whitney Houston?
In the mainstream: Adele, Sia, Ariana Grande, just to name a few.
> I even saw a documentary on autotune where a music executive remarked that they don't look for great singers anymore, because the sound engineers can "fix" it. They look for pretty people.
That was never different. Madonna is an absolute terrible singer, for instance, and that was fixed long before autotune existed. For recording, you just make heave use of vocal comping. Live, you can use a combination of (soft) playback and background singers.
But at least Pop was never about "perfect" voices, but unique, recognizable voices that can convey emotion, and that hasn't really changed. Bowie, Björk, Leonard Cohen, Thom Yorke, Damon Albarn, these are simply great voices, but they can barely hold a tone.