Well that's all true, we don't actually know what the real filters are, are we already past them, or are they still ahead of us? Certainly people have speculated about this for a long time, and I won't pretend to have any more real answers than anyone else. But honestly, I'd have a hard time believing that the really rare event, that the great filter lays somewhere between the development of the brain and the development of the kind of intelligence humans have. It just seems like a relatively small jump (relative to all the other hurdles) between many of the smarter animals on earth and human beings. For example, many species use tools a whole lot actually. Only a few other species actually make tools or alter them to a large degree, but you know, give it 10 million years and see if that changes. Likewise, many species have languages, some species even give themselves names, so they can intentionally address other individuals in their social group.

If you don't mind a bit of total speculation on my part, in my opinion, the explanation to the Fermi paradox is actually pretty simple, there really is no paradox. Intelligent life is probably relatively common in the universe, the reason we don't see aliens all over the place is that intelligent life thrives too well for that. Once a species is capable of traveling other stars, it's just a matter of time before they settle most of their galaxy, like within a million years (which is very quick on evolutionary scales). We're just the first intelligent life in this galaxy, we can assume this because if there were others, they'd already have colonies right here on earth, because it's a great planet.

To double back on the great filter though, my best guess about which events might be truly rare, my money is on Eukaryotic life and mitochondria. That feels like a real freak accident, as well as an absolutely vital requirement for complex life.