Here are my two biggest issues with this uber.
1st Gyua will spawn tornados and if I stand in them I get oneshot. If I pass trough its fine. The problem is that either the tornados are in the wrong possition due to some kind of visual bug or I am in the wrong possition due to desinc. In either case I would stand on those by accident and die instantly.
2nd is that Gyua would sometimes knock me back into 100 whisps and I would die instantly. Whether this is due to Gyua blinking on me or performing some kind of abillity I don't know, but it's quite random and in random direction. If I get knocked away from the whisps it is fine.
With the standard strategy of running around in circles and dpsing while avoiding the whisps these two events make the uber a pure luck draw. If you are lucky you kill it but it will take a long time before neither of these happenes.
I found a better way of dealing with this.
After Gyua pounces you should teleport and stand just at the edge of where you can se the boss nametag so that you don't get pounced again. Whisps will fallow you but you won't get pounced. After you pull all the whisps away, go back and dps the boss. Walk as little as possible and tank Gyua and whisps while you dps. When Gyua spawns too many whisps for you to tank, dissengage and repeat.
This strategy deals with both of the problems and I was able to kill Gyua pretty consistently this way while I didn't get a single kill using the standard strat in 20 tries.
Here is a vid of the kill
https://www.youtube.com/watch?v=3ivd-yxTucAAt 1:50 you can see the visual bug of the tornados and how I die to it. Later you can see how this strategy works.
This boss is op for lvl 125 and should be reworked, but untill now I hope this helps.