Ez had around 1.8-1.9k health in the first video?
700 from AD crit. ~250 from Shiv Crit, 700 from Q AD passive. ??? from Q Soul passive (can't see how many souls he has, assume over 150 given time-frame and results)
That seems fine to me, given the lack of resistances that Ez had, and the fact that, in all likelihood, EZ would have 2 shot Thresh (in roughly the same time and from a safer distance thanks to his own skills) if the situations were reversed.
Also, you should have magic damage turned on in your UI, would make it a lot easier to parse that sort of data.