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.