You seem to believe that everyone is mature enough to hear bad news, delivered objectively, and accept it without blaming the messenger, and without dismissing it because it doesn't conform to their wishes. I wish I had your luck in bosses.
In some, you actually have to "earn your place" in the company, and most recommendations I've seen are "keep quiet and listen".
I'm about 3 months in at a new company and starting to see areas for improvement. I just make a note and keep my mouth shut. In another 3-6 months I'll have earned the right to start diplomatically suggesting some of my ideas. For now i just try to understand the thinking that went into decisions that resulted in our current state.
If you want to go into a new organization and "be disruptive" and you're not a management consultant, be prepared for the likely outcome of failure.