I haven’t read the articles yet, but is this generated on-device, or at Google’s end? If it’s on-device, then it’s not so bad, other than being an unnecessary waste of battery life that most people haven’t asked for. If it’s being done server-side, then it’s obvious that they are fairly aggressively processing the content of user e-mail messages, and that should definitely be opt-in.
It is even worse if they are then also recycling all of this e-mail data back into training their models. Some people communicate somewhat confidential details via e-mail, and it’s not the sort of thing that a company should be able to use for it’s own purposes without permission.
I don’t use any of their mail services myself, but there are businesses I deal with that re-direct all mail sent to their domain into one of these services (maybe even consumer Gmail). In such cases, I have little choice, and you can be sure that Alphabet won’t care that they don’t have my explicit permission to process the content of my messages.