Yeah, basically the fundamental issue here seems to be that Google seems to see extension users as “Google’s customers” for them to experiment on directly, rather than seeing extension users as “customers of the extension products of whom Google happens to supply the platform for”.
In other words, Google sees themselves as the “B” in B2C, while extension developers see Google as only the first “B” in B2B2C. Extension developers see Google as skipping over the second “B” in not setting clear deprecation timelines that apply to every “C”.