HHI and Simpsons are neat new finds.
There's also this other variant of the Simpson's Index: https://www.thesimpsonsindex.com/
There's also this other variant of the Simpson's Index: https://www.thesimpsonsindex.com/
If the US had functioning antitrust laws it would be looking at their margins and be considering whether to break up some of the existing players, not considering when allow even more mergers.