1. Microsoft: MS was never interested (until it was far too late) in having a standards-compliant, performant browser. It was a spoiler move to keep people Windows dependent.
2. Mozilla: I honestly don't understand what Mozilla is doing other than raising top exec pay while Firefox users go down [1]. As best as I can tell, Mozilla is the Yelp in this situation. Yelp has spent over a decade extolling the evils of Google while doing absolutely nothing to improve their product. It's a great way to collect a fatter and fatter paycheck but you're ultimately doomed.
3. Apple: Safari has almost always been bound by its own ecosystem. It's dominant on iOS because you have no other choice (for now; you can install other browsers but they're still the Safari engine basically). A lot of people use it on MacOS. For a brief time there was a Windows port but it died. This doesn't seem like an area that Apple wants to compete in. I mean at the end of the day Safari and Chrome share a common Webkit lineage.
So I see a lot of failure, lack of prioritization, missed opportunities and finger-pointing in this space so is it any wonder that a massive engineering company has been able to dominate this space?
I don't see us repeating the IE6 era however. The Internet is core to Google's business in a way that it never was to Microsoft.
That being said, I think this is one area where government intervention may well be needed sooner rather than later. Google has (and continues to) use their properties to advance Chrome (IMHO) eg [2].
There can be a fine line between advancing the browser space and simply crippling your competitors.
[1]: https://calpaterson.com/mozilla.html
[2]: https://mspoweruser.com/engineer-accuses-google-of-sabotagin...
Depends on what your takeaway from the IE6 era was--if its that MS abandoned development and the web stagnated, then I think you're correct. However if you takeaway was that too much power was concentrated in a single private entity who has the defacto ability to control development and standards and channel them towards their best interests, not the users, then I think it would be the IE6 era all over again.