Yeah I know HN is going to hate me for saying that.
If a big company and a few small companies all have identical costs for producing a product, society is better served by having it produced by the few small companies than the one big company.
Once "better served" is quantified, you know the coefficient for taxation.
Make no mistake, this coefficient will be a political football, and will be fought over, just like the Fed prime interest rate. But it's a single scalar instead of a whole executive branch department and a hundred kilopages of regulations like we have in the antitrust-enforcement clusterfuck. Which makes it way harder to pull shenanighans.