Corporations in the 19th century directly controlled their own private armies, navies, police forces and towns. The power of corporations is certainly a lot less than it used to be and even the power of corporations to influence politics is decreasing as well. They certainly have far less control than they did 50 or 100 years ago.
That said I think there is enormous value in extremely large corporations. For a lot of next level stuff that requires huge long term investments, only very large corporations can field the capital investment for long enough to make it worthwhile. Think the pharmaceutical industry in the US. To make a new drug requires millions of man hours, years upon years of time, billions of dollars of investment, and even then it is not guaranteed the drug will end up even working. Small sized firms are simply not able to go into this market because it is a market that can only involve massive sums of money. There is a gargantuan initial input and the hope of a gargantuan eventual output.
Google which you mentioned is another one of these. By having such a huge amount of data on the same network it becomes possible for the large scale streamlining we have seen of the internet. To afford this enormous project it is undertaking it needs to be able to have a massive income. If youtube ran by itself its profits would be reduced and they would be more constrained since they lose a lot of valuable directed traffic given to them by google. You would see worse services on youtube and on google because they would lack much of the support of the other one.
Not to mention how companies are going to behave when they know that their own future prospects are going to be demolished upon arrival at a certain figure. Do you count cross company partnerships as one company? What about long term trading partners? I think there are a lot of problems with your whole argument.
TLDR Lots of thing out there that require vast inputs which only the largest companies can do (think space travel, medicine, large scale data analysis like google). If you stop those companies from existing progress becomes much, much harder.