As a thought experiment, there's a big difference between "3 companies share 70% of a market, while 30 companies sharing the remaining 30%", and "30 companies share the whole market, none being larger than 8%".

In the former example, there's far more pressure on the smaller companies, which is why in such a regime people expect more consistent quality from the big guys, and the smaller guys are often boutique in some way (=offering something unique in their service/product in order to be able to compete). Small guys have a hard time standing up to big guys.

On the other hand, in a regime where no one becomes that huge, like the latter example, there's still pressure, but the competition is fair, just like if all the companies were similarly big (except that you can't have that many big companies in a single industry, by proportion definitions).

Realizing this drove home why inconsistent antitrust enforcement appears to produce bad results. Because it leaves us in the state of the former example. It's also unfortunately the intermediate state of getting serious with antitrust enforcement.