I really don't understand your perspective.
To me it seems:
He couldn't build consensus within the org around his opinion (critical skill in a Senior PM role). Regardless of the underlying issue, it seems he can't rally people around his idea. That makes me think either A) the idea is no good or B) you can't rally people very well.
He didn't look ahead - His actions and disagreement with his manager led to his departure. We only have one side of the story here but im guessing him and his manager didn't get along often.
After departure( i get that he's bitter) he decided to release this confidential information. Even communications from Discover personnel that have nothing to do with the issue - I have an issue with that and would not trust this individual.
I am not defending Amazon or Management, merely disagreeing with the notion that this is an individual you want as a Senior PM. All in all, it seems this employee/manager relationship failed big time, and I would put some blame on both sides.
My assumptions here: NCA - not relevent. This gets agreed upon in advance (cont...) complaining about this after the fact changes how professional I view the writer.
Discover - Unless Kivin was the owner of this relationship, I don't believe he had enough information to go on here.
Team - Priority on needing to fess up to the client immediately is different from fixing the issue. I don't think these are the same issue.
Departure - Kivin entered negotiations on severeance here. Im
edit: I somehow submitted incomplete response then got distracted.. added (cont..) to denote separator of edit.