Yes, the Windows store is pretty awful and I feel like most Windows users have been installing software this way for a while (myself included).

I believe all of my current software besides games were installed this way.

To answer your first question, yes, quite a bit.

Yes, because there's no real choice. Only installing from an app store adds a little protection, but not much. The fundamental issue is the design of desktop OS' security models, which are focused around protecting local users from other local users, not around protecting local users from untrusted software.

(More than happy to hear suggestions for easy-to-use sandboxing for desktop software. The whole situation makes me quite uncomfortable.)

Not throwing away 30% of your revenue is a pretty good reason to still allow people to download your product from a website.

...yes.

(I should probably change my ways.)

(Microsoft could allow the store to be less terrible)

What's terrible about the store?

You can digitally sign your executables to increase trust.