It's certainly been in there for as long as I've been using Windows 10; not sure about before that. It was super-frustrating because it affected both keyDown and keyUp, and it was also completely inconsistent.
I can, however, if I squint, just about see the argument for why it's taken so long to fix: I suspect it probably wasn't seen as that valuable for the kind of apps and sites that Microsoft think people mostly use the web for. Thing is, get off the beaten path slightly, and you find people using the web for all kinds of interesting and creative things: demos, games, music players and editors, emulators, synthesizers and instruments, image and video manipulation.
And there is a school of thought (to which I don't belong) that says all apps should run in the browser. But if that's ever going to happen, massive and inconsistent input latency of any kind is not something that can be tolerated. Even if we don't go that far, and I suspect we won't, there are still a wide range of web apps for which unpredictable input latency is not acceptable.
So I suppose what I'm saying in a very long winded-way, is that I agree it shouldn't have been there for so long, although I don't think I'd call it unprofessional.
