With Google and SEO I see it more in the monopoly camp though. The existence of other big tech companies doesn't break the monopoly Google has by owning search, ads, analytics, et al under the same umbrella.
We've seen the legal gymnastics around market definition for monopoly purposes.
But it's harder for Google to make the case that it doesn't own at least a big chunk of {mobile OS} or {mobile app store} market share.
They can argue +/- a few percent over methods, but "We don't have a substantial market share" won't fly.
In this case though, it still seems like a more simple monopoly only with google. You don't need to consider other companies when the issue is related to the black box of search rankings.
If a few actors control the bulk of a market... wouldn't the same redresses be appropriate whether or not they're colluding?
We should make companies want to stay at a competitive market share instead of taking over their markets.
If we think free markets are generally going to move in the right direction, we should just want companies to want to fill market gap and outcompete. I don't agree we should make companies do anything though, at most governments should be tweaking incentives to attempt to push companies down a path without directly making them go there (even them I'm not sold that approach is worth it).
It’s possible the only hope is a painful one: a major market crash caused by greed and excessive consolidation, the kind of crash that would trigger a 21st century new deal.
The consolidation of power in the US government is the root of many of our problems, I don't expect that same government to solve it by grabbing even more power a la the new deal.
The US regulates monopolies.
The US regulates utilities, defined by ~1910 industries.
It doesn't generally regulate non-monopoly companies that are gatekeepers.
Hence, Apple/Google/Facebook et al. have been able to avoid regulation by avoiding being classed as monopolies.
Imho, the EU is taking the right approach: also classify sub-monopoly entities with large market shares, and apply regulatory requirements on them.
I'd expect the US to use a lighter touch, and I'm fine with that, but regulations need to more than 'no touch'. It'd also be nice if they were bucketed and scaled (e.g. minimal requirements for 10-20%, more for 21-50%, max for 50%+).