Windows 10 actually fixed that problem. For the most part, apps can't change defaults silently anymore. The settings page for changing default apps has also been revamped, so it's a lot easier to use than in previous versions.

It would have been marvelous if Microsoft stopped right there. Instead, they chose to annoy users with an unskippable dialog box whenever a new app is installed that claims to know how to handle a PDF, JPG, or whatever. Fuck it, every app and their dog knows how to handle PDFs these days. I'm just waiting for the day when Windows suggests Slack as the default music player.

Slightly off-topic, but it would be an epic april fools joke if Slack actually implemented that just to troll Windows users.