The problem is how you break up global companies with the kind of reach of some of them.
Tesla is really only large in market cap; in size and sales they certainly aren’t bigger then Ford or GM or Toyota or VW.
FB, yeah, strip them of Insta and WhatsApp, I’m cool with that, but beyond that?
Amazon? I dunno. How do you downsize that?
MS, there was some targeted anti-trust stuff there already, someone smarter than me can opine on more
Berskshire, what do you do? Bar him from investing more?
When looking at a company for possible breakup, you should ask themselves what they are doing that is anti-competitive, and how do you address it.
Nothing was really ever done to address Microsoft (the administration changed before the DOJ could take them to court back in 2000-2001). Microsoft makes the operating system AND a suite of applications. That means that their application division will always have a leg up on other companies developing Windows applications, since the application and operating system divisions are in constant contact. The application division had input into the interface design of the operating system. The operating system API (application programming interface), and it's continual evolution, is made available to the application division before anyone outside of the company. Finally, there was evidence that Microsoft was maintaining two Windows APIs: the one for the rest of the world, and a faster, better performing one that was only available to their own developers. This is how Lotus 1-2-3 and Word Perfect died: they literally could not beat the performance of Excel and Word.
Looking at Amazon, a similar situation exists. Amazon is an online retailer, akin to a mall. So, imagine if the local mall also owned it's own stores in direction competition with other tenants. That means those stores have less overhead costs, allowing them to undercut their competitors. That is what Amazon is doing by owning the platform and being a vendor on it. Now, imagine that the local mall decided to start manufacturing it's own goods in direct competition with others, selling them at a loss, subsidized by the enormous profits of running the mall. That is what Amazon is doing with their own Amazon Basics line of goods.
Downsizing is actually not the answer. You break a giant up into multiple companies. Microsoft Windows is one company, and Microsoft Applications another. No collusion may occur between the two; it must operate the same as any other app developer's relationship with the operating system developer. One could maybe make the argument for Microsoft's hardware, but no one buys their phones, and their tablets are a very small part of the market. Basically, Apple and Google have run away with the mobile market, and they are their own arguments for busting up that I won't get into now.
Amazon should be
four companies. Amazon the online storefront, Amazon the online vendor, Amazon the manufacturer of goods, and Amazon Web Services. The way they all work together has choked out most of the eCommerce on the Internet that used to be there before. Sure, there are other big vendors, but all the small ones have fallen away, forced to operate in Amazon's space for much less than they made before, leading many of them to close up shop entirely.
THAT is how Jeff Bezos, Steve Jobs, Elon Musk, and Bill Gates became billionaires. Through monopolistic and predatory business practices that unfairly squashed competition and took and larger and larger share of the profits. If you eliminate that behavior, you eliminate billionaires without having to ever pass a law to target them for high taxes or the like. And innovation NEVER occurs in big companies; all of the innovating of these companies occurred when they were smaller (in the case of Tesla, before Musk bought it). Past a certain point, it is simply a machine to generate enormous wealth for a few people. Small business is the real economic engine of job creation and innovation.