The heart of the matter is what the ethics experts see as an attempt to suppress criticism of ethical problems with Google's technology. So yes, it's very much an ethics breach.
Whistleblowing need not be only about crime. It can just be about harm. [1] Indeed, with new technologies, regulation often has yet to be written, so whistleblowing can only be about harm.
Dean said in his letter that the paper didn’t address relevant literature related to the subject that the authors weren’t aware of. To me it doesn’t seem that the reason is that it besmirched Google, but that it wasn’t complete.
Also the article wasn’t an ethics breach type of article and internal so I’m not sure what the legal protection would be. I think if the employees had some evidence of illegal activity then they would be protected.
If this paper would be considered an ethics breach then I don’t think there should ever be relevant protections.
You seem to be conflating ethics and legality. The two are only hazily related. And yes, of course the executives who hired ethicists to make the company look good disagree with the ethicists on what constitutes good ethics. But your notion that "No one in this scenario reported an ethics breach" is incorrect. We can't of course know the truth of the matter, because Google insists on keeping relevant facts hidden. But unless clear evidence shows otherwise, I'm going to believe the ethics professionals, not the executives whose identity and financial success are strongly bound up with making their company look good.
There are whistleblower laws now but they apply to illegal actions.