Correction: That would be Games for Windows Live and the premium multiplayer they tried to force upon PC players last decade, actually.
For the Windows Store, I’ve personally had very few issues with it gaming-wise, and so do most of the folk I know.
Others, sadly, have had issues, and it sucks that you’re one of them.
As I mentioned, Iron Galaxy was a company contracted to develop the game, and their contract ended back in either 2017 or 2018. Their involvement with the project is done; they haven’t wiped their hands of things they’ve literally completed their work. The game and the property are owned by the publisher, Xbox Game Studios, not Iron Galaxy, and any further support is from them. The recent 3.x GB Xbox One patch for the game was done by Xbox directly, not Iron Galaxy, for example.
That one guy, who did work on the game, was helping people as a courtesy and because he’s a good guy, he wasn’t being paid to do this at this point. He appears to be an independent contractor as well.
For your own issue installing the game, it still sounds to me like it’s one of two things: 1) something on your system specifically, or 2) an account issue. A few more things I’ve thought of:
- You mentioned you are using the same account you bought the game with on your Xbox One. By chance, have you moved and are you in a different region? I’ve heard a region change can fudge stuff up.
- Did you ever install the game on your PC via Xbox Game Pass? I’ve heard that doing so, and then buying the game, can create a duplicate copy that can fudge things up. I don’t know how to fix this one, but people on the Killer Instinct Discord do.
- Have you tried resetting the actual Microsoft Store App? Details can be found on the troubleshooting page here. Step 7 helped me in the past with a non-gaming related Store issue.
Here’s a Support Page on troubleshooting game installs on Windows 10 specifically. The “Still having problems” section may apply to you.