The lack of QA isn't felt right away. They are accumulating tech debt, which mean problems are becoming more frequent and harder to solve over time until they fix the fundamentals, and it doesn't feel like they intend to.
2. "becoming more frequent and harder to solve" how much more frequent and harder? Things works pretty fine during Windows 10, but these days I run into a bug in Windows 11 every other day myself.
It would be a surprise if this has more to do with QA from 2014 than vibe coding.
I doubt "studies" exist and proving every little assumption takes too much effort as per Brandolini's law.
For example: https://www.zdnet.com/article/microsoft-on-windows-10-annive...
These things have been keeping happening.
They won't fix the fundamentals, the next API layer will just be built over the broken one.