I didn't watch the video, but I don't put a lot of stock in Kurzgesagt, but we've got evidence of things just instantly dying thousands of miles away. I don't think there was a hundred years of total darkness, but there was probably at least a decade where we weren't getting sunlight on the surface. Lack of photosynthesis DID make a lot of plant species go extinct, and the ones that survived had better adapted life cycles. Remember also that plant seeds can stay dormant until conditions are right.
"Our ancestors" were not anything like us, and their survival isn't indicative of our ability to survive. The things that survived were things that were less impacted.
Something like the K/T event happening has a lot of unpredictable factors involved. We don't know what's going to end up in the atmosphere or what kind of aftereffects there will be, where earthquakes will happen or volcanoes will go off, or what effect other species dying will have on the whole food chain. It's going to look like Chrono Trigger's bad future for a long time though, and that's not good for anything bigger than a gopher.