I don't think megacorps should be "destroyed". On the other hand, I do think that a whole lot of those countries grew up taking advantage of mechanisms and data that they seek to exclude others from having by use of their market power and restrictive contracts, and this should be prevented.

E.g. back to Meta, etc: they scraped everything, everywhere for a long time, and it was a big factor that lead to their rise. Now they seek to control all the data in their fiefdom, and use the power of the legal system to enforce EULAs to prevent others from doing the same.

Why? Because economic entities with market power underproduce, overcharge, and fail to innovate and meet their customers' needs. They cause deadweight losses through their inefficiencies. And an excess of concentrated power is just plain scary, whether an individual, a corporation, or a government wields it.

Of course, reducing some of the edge of market power at scale will result in a smaller maximum company size.