Would be more interested in sending it bogus data.

Strangling it to death with ad blockers isn't working (or at least is doing less than the self inflicted damage being caused by mismanagement over at Google).

How can we make its output completely wrong, instead of just incomplete?

I'll happily stick a "do not track” header (or the new one) on the bogus requests. In my book, they've been warned to back off at that point, so any bad outcomes from tracking the requests are on them.

FYI GA4 was released over a year ago, it seems it hasn't 'stuck' with not many people upgrading, at least with many people I've worked with. It is the default version when you setup a new GA property though.

Any mainstream adblocker will block it.