It doesn’t make garble sympathetic in the slightest. He’s been the alpha male of the “teen” dragons and has out performed every one of them. He was also going to win the gauntlet of fire and it required Spike AND Ember working together, along with a distraction of Twilight and Rarity in order to keep him away from the scepter. Why was it so important to stop him? Because his rule = Full on dragon war with equestria.
I’ve said this before, Starlight was going to cause catastrophic damage, but what was her intended goal? The removal of cutie marks. That’s it. She didn’t intend for Sombra to rule, for Chrysalis to win, for Flim and Flam to turn the world into a mechanized dystopia, or for the world to be burned into a barren wasteland.