Someone can be a savant in one area and a midwit in another. Another way to phrase this is that specialization of labour is common, and specialists don't generalize well outside their speciality. Or: knowledge transfer is hard. 

For instance, I have a family member who is very knowledgeable when it comes to geography, but they've sadly been infested with TV brain worms so they're hopeless when it comes to politics. Or another family member who is very good at MacGyver-eseque solutions to daily problems, but somehow cannot navigate to save their lives. Or a friend of mine who is consistently insightful when it comes to econ yet somehow doesn't know calculus. 

This sort of "spikiness" in capabilities is the norm amongst humans. It holds for me, you, and even those who are world-class. Like: 

1) Greg Egan. He has deeply impressive mastery of physics and geometry, produces some of the best SF known to man, and yet has silly takes arguing that intelligent minds cap out around human level or would naturally not be expansionist. 

2) Elon Musk. If we set foot on Mars, Musk is the human most likely to have caused it to happen. This isn't just business acumen. People who work for SpaceX acknowledge his engineering ability. So clearly a master of getting things done in (parts of) the world of atoms. But look at DOGE, where Musk burnt through huge amounts of political capital to no real end. 

And it's more general than that, really. Any one of the people I mentioned has their own areas of expertise in which I'd expect them (to some degree) to outperform others. But only in those areas. 

You would not go to Terrence Tao for medical advice, or for help designing your house or doing your taxes or so on. Sure, given time, he could do a better job than most experts. But obviously he's not going to do that. 

And yet, for some strange reason, I often see someone be incompetent in one area and then immediately generalize to a lack of competence in all other areas. Heck, I do this too. 

Now, obviously this has some merit to it. There is a g-factor after all, and if you see someone persistently try and fail to resolve an issue, that is evidence they just aren't that sharp. 

That's not a problem. The problem comes when you don't know what someone else cares about, where they've invested their character points, and then rule them out as a moron if they perform incompetently in an area they don't really care about being good at. This is an issue. 

Now, obviously you don't see most experts loudly giving stupid takes on topics you know a lot about, because you don't see most experts do anything really. But we're animals that build our models of the world from patch-works of lived experience, and sometimes our only lived experience with some groups of experts, or groups of people, come through seeing them from afar when they aren't in their elements. And that skews our perception of how competent people can be at their best. And when you're trying to make use of people, the best you can get out of them is what matters. 

Forgive them their midwittery, for they are also savants.