I think the reason you keep reiterating this is because once you realize that there is no legal justification to go after Google for this move under current US law, the only real solution becomes obvious: new legislation, and you really don't want that, because you know it will apply to Apple devices as well, which would be The End of the World.
(This is before Apple/Google lobbying efforts result in either the death of the bill or a bunch of exceptions allowing companies to do "notarization" or "developer verification".)
Antitrust law applies to any company of massive size that engages in anticompetitive conduct, not just companies who create "open platforms" [1], otherwise there would never be any antitrust cases. An antitrust case would be your best hope under current law, but it already happened and the remedies did not include a mandate to keep allowing unrestricted sideloading indefinitely.
Anyway, you're now moving the goalpost, because you were originally talking about a case based on the premise that they engaged in fraudulent marketing, not a case based on the premise that they currently hold a monopoly. The former would never hold up in court, the latter already happened but the remedies were insufficient to stop Developer Verification.
[1] The reason Apple wasn't forced to allow third party app stores as a result of Epic Games v. Apple was not because iOS is a "closed platform"; they simply weren't found to be a monopoly in the "mobile gaming transactions" market (which does not preclude them from eventually being found a monopoly in the "mobile app distribution" market).
I already replied here: https://news.ycombinator.com/item?id=45512015
I think the reason you keep reiterating this is because once you realize that there is no legal justification to go after Google for this move under current US law, the only real solution becomes obvious: new legislation, and you really don't want that, because you know it will apply to Apple devices as well, which would be The End of the World.
If you want to see what the solution to this problem looks like, take a look at the bipartisan App Store Freedom Act: https://www.congress.gov/bill/119th-congress/house-bill/3209...
(This is before Apple/Google lobbying efforts result in either the death of the bill or a bunch of exceptions allowing companies to do "notarization" or "developer verification".)