The Fermi paradox depends on having an estimate for the number of intelligent and communicative species in the universe - which in turn requires us to look at the "Drake Equation" which provides that estimate.
The Drake equation includes the following terms:
- the average rate of star formation, R∗, in our galaxy,
- the fraction of formed stars, fp, that have planets,
- for stars that have planets, the average number of planets ne that can potentially support life,
- the fraction of those planets, fl, that actually develop life,
- the fraction of planets bearing life on which intelligent, civilized life, fi, has developed,
- the fraction of these civilizations that have developed communications, fc, i.e., technologies that release detectable signs into space, and
- the length of time, L, over which such civilizations release detectable signals,
Astrophysics provides good estimates for (1), (2) and (3), But (4),(5),(6) and (7) are all wild-assed guesses. We don't know what exact process got us from inert chemicals in a warm amino acid soup to the first replicating DNA/RNA molecule. We don't know why (for example) the dinosaurs never developed civilization - despite being around for far longer than we humans have been here. We have no clue as to whether other civilizations would be so fascinated with technology as western europeans and the chinese were in the 1700's and 1800's - given that other civilizations generally didn't care much about that. We have no idea how long a technologically advanced civilisation might last.
So the result of the Drake equation is pure guesswork - which means that the answer could be that there is such a low chance of there being intelligent, communicative life that it is unsurprising that we are the only one...and if that's the case, the Fermi Paradox evaporates. But on the other hand, if we ever do find simple life (for example on Mars or the moons of Jupiter and Saturn) - then we suddenly have a much larger estimate for term (4). Term (5) will only be known if we find the results of industrial pollution in the light spectra from the atmospheres of distant exo-planets. Terms (6) and (7) can only be known if we get messages sent to us by aliens...which would render the Fermi Paradox moot.
What's kinda cool for me (but evidently not for FE'ers) is that the odds are good that we'll get the answers for (4) and (5) in my lifetime. But (6) and (7) - I'm not holding out much hope that we'll ever get good estimates for those.
So while the Fermi Paradox is an interesting "thought experiment" - it doesn't help us make any deductions about the universe. You don't need to "find flaws" in it...the flaws are inherent in our lack of knowledge.
But from an FE perspective - there are no other large bodies out there that could maintain life - so it's all irrelevant anyway.