Well that’s your opinion. 
I would love to have sliders. For one, I don’t like how every male character looks castrated. Saints Row has gender-based sliders, why not WoW? Yeah it would mean the customization system might need an overhaul to implement the sliders, but it would be a HUGE step forward!
Imagine everyone but gnomes having a height slider! Imagine an 8 foot tall Blood Elf Warrior with thick rippling muscles charging at you in PVP! That would be nightmare inducing!
If height is the only thing with a slider, I’d be fine with an added switch to pick a different voice. I would make my Blood Elf warrior have the voice of Vic Mignogna. The guy is super nice, exceptionally professional, and talented to no end! It’d be a way for Blizzard to give the guy work too, given Ron Toye has committed numerous crimes with tortious interference!
Vic Mignogna as a male Blood Elf voice option! He can double-dip and also do undead too! He did his own personal WoW commercial with his own undead warlock! He’d be a great addition!
More voice talent to give us options for different voices! It’d add variety to the voices we hear! Imagine hearing Jim Cummings as the voice of a Highmountain? Or hearing his voice from a pandaren? EVEN A GOBLIN!
There are so many voices that would be fun to hear as character options! Maybe even have some unique VA quotes.