As usual, people always seem to foreget that in this universe, what happened once, happens all the time and we are not special.
I get the convergent evolution point, but so far the story is that 1) life arose very quickly 2) then proceeded to do very little for billions of years. If that's true, then it's bad news for the possibility of complex life being common.
This is understating the feats of unicelular life. Those tiny organisms essentially terraformed the whole planet in those billions of years, oxidizing nearly all the iron close to earth surface, burying most carbon and then pumping so much oxygen in the atmosphere that at a point it comprised 30% of Earth gaseous envelope by weight. I wouldn't call that very little. To come close we'll need at least to terraform Mars or Venus, to match the feats of our microbial forebears.
Well, it's quite possible that once it happens, it voids any chance of it happening again just because life filling that niche already exists. If so, it only happens once, and this says absolutely nothing about the odds of that first occurrence.
> what happened once, happens all the time
That's a fallacy people do all the time here when talking about exobiology. It's basically states that all small numbers and all big numbers are alike, and that all small numbers are like the inverse of all big numbers.