I'm sure by now the OP has defeated Patient Zero, but I wanted to give my experience with him. I am a 99% PvE player, so I have crappy gear, and haven't played much in the past two years. The first time I tried Zero (2 days ago), I brought Quinn to help heal my Lvl 52 Immortal Jugg. Got my butt handed to me, thrice. I left and went to level for a while. Came back a day or so later as a Lvl 54 and used Jaesa. We beat him into submission within 2 minutes. I have no clue if updates since then have nerfed him, but being a higher level obviously helped me.