Sure, but that's the example of monopolies facing competition when they turn bad. Sometimes that takes a new platform shift, other times its just a better product, but either way if there's new value then the monopoly breaks down.

I think if anything, the problem today is companies that could be challengers just end up selling to the very incumbent they're competing against.

In the instances you’ve described where “monopolies” haven’t dominated the market, they were not actually monopolies because they didn’t have total ownership of the market.

A company can be a tech giant and still not be classed as a monopoly. Which are the kind of examples you’re think of.