Of course, then Microsoft faced a major lawsuit related to their browser monopoly. That seems highly unlikely in today's regulatory environment.

Whatever happened with Microsoft buying Activision?

In general I agree with you though, my above example likely only exists because there's another huge corporation involved.

For new businesses trying to edge a way in the market, yeah good luck unless you've got something novel.

More that controlling a platform is no longer seen as a monopoly position. If Apple can get away with effectively driving Tumblr out of business and taking a cut of everything transacted on its platform, it seems unlikely that regulators will pick out a web browser as the hill to die on.