False. The law actually changed because judges noticed that the law as it was in the books was pretty nonsensical and totally arbitrary.
It was mostly created, pushed and used by a group of progressive to go after their political opponents. Its well documented (even if people choice not to remember this part) that this was very much PR and protectionism of businesses that were afraid to be driven of the market by the larger more efficient companies. The first anti-trust law in US history for example was quite explicitly passed to restrict the centralised slaughter house industry from driving all the local butchers out of businesses)
The new interpretation that has been adopted requires that you can show consumer harm. I actually have credible evidence that people are getting overpriced.
> Many of our concerns about antitrust would be assuaged if regulators started keeping separate markets separate.
That is very easily said but practically impossible. And even if it is possible, it would be massively harmful because some of the largest changes in the history happened because or were at least massively supported by companies bridging, merging, combining, integrating different markets.
In fact what you describe is pretty much called 'Indian Socialism' a form of 'Socialism' that was very in vogue with British elites after WW2 and India served as a nice place to test this since many of the Indian leaders had an English education and agreed with it. They had a sort of 5 year plan that attempted to plan how many companies could be in what market requiring licences to go into or out of different markets.
Those licences were of course a perfect tool for the state bureaucracy to get bribes from all business people.
> Or requiring platforms to provide third-party-friendly APIs.
Again, said very easily. Have you considered what that would mean? It would mean government regulator would have to go threw each layer of the software and each application and define adequate rules about what sharing would mean. This is a political insanity specially in a democracy.
Now you could argue, that it should all be made by some loosely controlled government bureaucracy like the Fed. An API tzar but how that would end is pretty easy to see.
I would agree that it would make sense for government to support and insensitive the adoption of open standard that were created and adopted by people and companies in the market voluntary.
If you want to use state power to force companies to support open standards it can not be on a ad-hook bases. You would need to think about a specific general law that could be applied to everybody and that does not involve concrete technologies or companies. That would be pretty hard because I think once such a thing is written most people (at least in here) would oppose it.