Over the past decade, I've been dealing with sorting out a rare and difficult to diagnose medical issue with a family member. Over this decade, I've learned what I consider a very important lesson and one that I often find myself having to re-apply and to have discussions with providers over.
What you call something matters a lot less than what you do about it.
What I mean by this is when you're in the weeds of "not in the first few options for diagnosis", a lot of conditions have a lot of overlapping symptoms. You might get a diagnosis for some condition, and then as new evidence comes to light, that diagnosis may change. After a while you start to doubt any possible diagnosis and even when you get one, you spend your time worrying about "What if I'm wrong? What if I don't have X?". The thing that's important to remember though is that for a good chunk of the symptoms that all of these conditions have, the treatment for them is exactly the same. It doesn't matter if you have condition X, Y or Z if the treatment for symptom Q is the same for all of them. That doesn't mean an accurate diagnosis isn't important, it very much is. But it's only important where the treatment options would differ. But if you want to resolve symptom Q and the treatment is the same, it just doesn't matter what you call it.
The same thing applied to malice vs stupidity. Unless there's a very different action to take to mitigate the problem, it doesn't matter which one it is. Lets take your example of someone taking credit for your work in front of upper management. If this was stupidity what would you do to mitigate the issue? You'd do more to document what you're doing. You'd make sure you have a chance to speak for your own efforts. You'd make sure that your contributions are more visible. You might get a neutral party involved in keeping an eye on things. You might gently correct your co-worker if doing so was appropriate in the moment.
So what would you do if it was malice? Probably all of the same things right? About the only difference in what you do might be whether you talk to the co-worker about it, or talk to HR. But beyond that, everything you'd do to mitigate the issue is more or less the same. And whats important is that the issue you have is that credit was taken for your work. Really in the end it doesn't even matter whether it was stupidity or malice because learning which it was doesn't get your credit back. And accurately labeling it doesn't stop you from losing credit in the future when it happens again.
But there is one personal benefit from assuming stupidity, you can feel less anger. It's a lot easier to be objective, and stay focused on your real goal and the problem you really want to solve when you don't feel like you're actively being attacked. So whenever there is ambiguity, and the actions you would take to mitigate the real issue are the same, why choose the label that increases your own stress and anger levels and makes you more likely to retaliate in a way that actually back fires on you because you're reacting in anger.
Which again isn't to say that you should be a doormat. But you can set boundaries for yourself and take actions to accomplish your goals without getting mired in judgements of other people's actions. Their feelings about it and their motivations aren't my concern, my concern is taking care of myself. I don't need them to see things my way, or admit to wrong doing to enforce my boundaries and take care of myself. And I can take care of myself a lot better if I'm not angry and stressed out.