> You are overestimating the effects. Or just forgetting what the situation really had been
That may be, this is speculative history fiction after all.
The seeds for MacOS were planted when NeXT was founded and successfully created its successor. Apple might have turned out very differently in the late 80's and 90's has NeXT been done in-house. Lets just change one thing for speculation purposes though.
I can see how 286 protected-mode could have thrown a monkey wrench into the design but Xenix was ported to the 386 and available at the time a switch over could have been made from DOS. Compatibility could have been maintained with Merge for example or some other DOSBox-like technology created. Windows could have been designed for Xenix instead of DOS.
The rest of the systems turned out to be small fry or have fundamental flaws either technically or in the management of the companies supporting them. I don't think the winners and losers of the 80s-90s would have turned out differently but there was an opportunity that was missed.