In practice I think he is right unfortunately. Most people would just run Chrome and more websites would require Chrome since they could just tell Apple users to deal with it, making the mono-culture even worse.
Yes I have, I worked with it for years, there's the officially supported standards and then there's the buggy reality you have to deal with. I've encountered bugs with backgrounds, zIndex, videos, forms, localStorage, SVGs, all basic browser features.
Then Safari also is the last non-evergreen browser so it's the slowest to update compared to all the other browsers. If you have a bug, there's a good chance you'll have it for years
Evergreen refers to the speed of update, your average iPhone user takes one year and half to update. Your average Chrome user is updated within 3 weeks, your average Firefox user within 4 weeks.
Call it with another word if you want but Safari is on a league of its own.