It's a skillshot that's really easy to dodge. Play Xayah, keep an eye on him, and ult immediately when you see him start dashing at you. Or flash to the side. Or dash away. Literally anything. It targets a small circle and knocks up everything in that area.
Looking at your op.gg, you seem to be a Kai'Sa player who rushes attack speed instead of getting Stormrazor first, causing you to deal no damage in the early game. You also start Doran's Shield, even though that's a really bad item to start on an ADC unless you're terrified to death of your lane opponent repeat killing you, which you never should be if you're on your main champion and know what you're doing.
Here's a thing you can do: mark Malphite with your passive, and then when he ults, ult ANYWHERE in his range and I guarantee you his targeting will push him past your repositioning from your ult and he'll miss. It has a small range, only hits the circle and not the path along it, and it's literally his entire champion. If he's building full AP and you're dying to him, which would explain the 1-shot, I really don't feel sorry for you considering that you play one of the single best ADC's in the game at countering him and still fail to. You clearly don't understand the game at all.