Does anyone else feel like 90% of the population is stupid?
To clarify here, I don't feel like I'm significantly smarter than most people, but I feel like people have a hard time doing any sort of thinking about stuff. Especially when it comes to verifying "facts."
If you "don't feel like I'm significantly smarter than most people" but view "90%" of people, which I think is well into "most" territory, are stupid then one can reasonably infer you're putting yourself into that category.
Additionally, what does stupid even mean? If I were to try to engage with the spirit of your question, I ironically find myself reflecting on a wise insight my uncle once gave me. Someone who would fall under "stupid" if I am to understand your question right. Anyways, my uncle once said that smart or dumb don't have an all-encompassing nature (IQ eat your heart out). Instead, one can be smart or dumb with respect to specific domains. My uncle knows a lot about guns, not so much about the internet.
So to answer your question, yes most people are "stupid" about most things, but are often quite smart in specific fields related to their life experiences. That's why we have experts in various fields of study. You and I are no different, and employing empathy seems to be the best strategy to bridging knowledge gaps with others, if that's your goal.
My take is most people have a lot more intellectual capacity than people think, but the majority don't know how to use it.
Trivial proof;
Ask somebody to solve a propositional logic question. Give them all instructions they need. Then ask them if some person cheated in a hypothetical social situation. The majority instantly solves the latter correctly, the majority has no idea how to handle the former. Note: social rules can be directly translated to propositional logic, the two types of questions are effectively equivalent. The same thing applies to advanced math like statistics and many other fields.
Humans have the capacity. They just don't know how to generalize correctly. They don't know how to deal with problems of an unknown form. The have a hard time following instructions if they feel to abstract. All of this can be trained, if people want to learn. Unfortunately most people don't want to learn.