The PC performance and price of the ultimate edition were definitely why I didn't pick it up at launch despite being a huge Forza Horizon fan. I would not be surprised if the poor performance was bad emough to affect sales for 3 and then for 4. A lot of people don't bother to say "well hey maybe they fixed it this time," unless they're already interested.You're an insider, you should know how PC games are selling on the Windows Store :p
If not, the Forza Horizon 3 leaderboards may give you an idea, since you can filter them based on platform:
https://forums.forzamotorsport.net/...nths-after-release-and-2-months-after-BM.aspx
According to this thread, 7% of FH3 sales were on PC, 93% on Xbox One. Although 7% is higher than I expected, I don't think it makes Microsoft's console business irrelevant. ;)
Edit: that thread was made 6 months after release, so these numbers may be different now because of Game Pass and FH3 + Store improvements on PC.
Also there's the windows store...