> complex highly intelligent life capable of space flight is extraordinarily rare in space and time

That feels right to me especially given the timescales we are dealing with when we consider things even just in a galactic context. Heck, even the timescales on this planet alone are such that there could be multiple complex intelligent life forms on earth separated by sufficient time that they are never known to one another! Not to mention the fact that there are intelligent life forms on earth right now that we barely understand. For all these reasons It seems to me that we are far more likely to come across an alien artifact than an alien, and we haven’t started looking for these.