> Will I be able to take screenshots at will on MY computer, or get a black screen because Google decides so?

It's not Google, it's the application vendor that decides so. And as annoying as I find it when I want to screenshot something from my bank app, the reasons behind that feature being available are pretty good.

> Given what Google has done on the mobile space

You seem to be missing the nuance that as annoying as some of those Google provided Android hoops are, they are necessary for the wider security posture of the average user (and there are more average users than techies that need to install random .apks) and, very very importantly, Google allow you to skip most of them if you know what you're doing. Considering the competition in the mobile space, it really isn't even close in terms of openness.