"We have extensively mapped the path of evolution that resulted in that life" just proves our sample set is statistically insignificant. One planet our of billions isn't proof of anything except what happened in our back yard. All life on this planet stems from the same root genome, and most vertebrates are tweaked variations on the same basic plan. The tiny bones in our ears are adapted from jawbones, for instance, and just because that happened here doesn't mean it's going to happen in the same way on a totally alien planet.
As to "So, the aliens in ST are probably the most realistic, ironically." Most realistic than what?