> then they could have easily hidden the required network-reading functionality behind a flag or "developer mode"
For all intents and purposes, that's basically equivalent to deleting uBlock Origin for 99.9% of the 29M users it currently has.
> only allowed it for a small set of manually-audited extensions like uBlock Origin
That would most definitely lead to accusation of favoritism. That would be just as annoying of a pipeline to maintain.
> The fact that they provided absolutely none of these alternatives isn't a coincidence
They delayed the release 3 times, it was first announced in 2020. The whole time, they were taking feedback and making changes. They made a ton of changes that made MV3 adblockers possible.