There are people out there bewildered by those of us who have strong operating system preferences. For most users, Windows, MacOS, Linux/Android, and iOS are pretty much the same thing. They let you connect to WiFi, install apps, send email, etc…. They show you icons you can click or double-click to launch an app.
I do think designers can go over the top. I could tell you stories. On the other hand, there is some line between design doesn't matter and "can't you see the difference between the two shades of black in this poster?" (Which is one of those stories.)
I should say as well that I've spent a fair bit of time in Asia and, to my Western eyes, a lot of conference materials look amateurish and make my eyes bleed. Maybe it doesn't matter much at the end of the day but I think it does at some level.