My main issue with her is the ult, but the main darts also require about 0.1 skill to use with the accuracy it has, and even when you react instantly, you still die to the poison, and if you don't for some reason, she will stealth again and kill you.
Skye isn't broken, she's just your generic pubstomp hero who completely loses any competitiveness once you go to an even somewhat higher tier of gameplay. Nearly every game has one of those.
Personally, I believe character concepts like those are just bad design: they only serve to infuriate new, inexperienced players while adding little to no value to the game once you go beyond that point. But oh well, every type of game for some reason needs to have a stealther, so what can you do.
District 69, the winners of the 100k tournament at Dreamhack played with a Skye here: https://www.twitch.tv/paladinsgame/v/88592236
At 2:30 there's a good game with her and they played her in most matches, they didn't play her in the Final though. Week 2 didn't have good coverage for some reason and I haven't watched the NA games.
My idea is to make her stealth like Heroes of the Storm, you could still see the silhouett of invisible heroes if they move aroud