Any value that something this large has, is in its ability to exhaust resources from the ecosystem, control the market, the workers and the ability to resist changing its behavior when better things come along. Companies exist in a system that should serve everyone and when an imbalance occurs the whole system morphs around them. They are no longer players but dictators, willingly or not. Their sheer size forces rules of the game in ways even they do not control.
Breaking up large companies isn't even about them. It is about us and the world we want to live in. Remember the wage fixing scandal between Pixar, Google, Apple and bunch of other companies in the bay? [1] They ultimately controlled where those people worked (and their horrible commutes), who they were friends with, what schools their kids went to and who they married. All because the execs at these companies wanted to maintain total control of the workforce and suppress wages. That is too much power for a company to have or wield. And these large companies due to their size alone are doing this on an unconscious level. On a conscious level they can do much worse.
Microsoft stagnated for what 10-15 years? But it isn't just MS that is stagnating, it is all the people in those markets. There were a bunch of us WITHIN the company that wanted the divisions repotted so each could grow on its own. If value is being lost when an organization that large is distributed to a smaller number of units, then the value is selfish, it only serves the org and not the system it operates in.
What is the end state if we let this continue? 20 large corporations in America and a field of small feeder gig economy vendors? We will all be serfs (NPCs) in a feudal corporate cosplay.
[1] https://www.theregister.com/2012/01/20/doj_emails_anti_poach...