Windows became the dominant OS because of demand from computer users; the problem was that Microsoft used its dominance in the OS market as leverage to gain dominance in the browser market. It is not just that the OS came with a bundled browser -- Microsoft deliberately and for no technical reason made IE a dependency of several unrelated Windows features (e.g. the desktop, the file browser, etc.). Most people received Windows pre-installed on a computer they purchased; had Microsoft not made IE a dependency of Windows itself, OEMs would have bundled browsers according to customer demand.
So yes, in fact, having IE pre-installed was a problem and ultimately Microsoft was forced to create this:
Which was ridiculously as well, just like the cookie thing.
"- Microsoft deliberately and for no technical reason made IE a dependency of several unrelated Windows features"
So?
But they did not forbid other browsers to run. People who wanted, could choose all the time.
And even if they would have forbidden it, I still think regulation is stupid, because it still keeps the status quo of Microsoft OS Desktop dominance.
(Luckily it doesn't matter much anymore) because when you regulate the worst things away, the base is still bad, but people have less incentive to change the platform for the better ...
So yes, in fact, having IE pre-installed was a problem and ultimately Microsoft was forced to create this:
https://en.wikipedia.org/wiki/BrowserChoice.eu