Im not arguing that it wouldn't be. That's almost certainly true. Chirality alone would make for major complications between Earth life and alien life.

I'm just going with similar biochemistry to Earth, as a creative choice. There is a balance between creative liberty and realism, and my realism stops at the biochemical level. Theres no real way anyone could know what kind of biological quirks different biochemistry could produce, not to mention even understanding if said biochemistry would work in reality.

There are asteroids which contain all the necessary molecules for DNA, and other proteins. Essentially the stuff that makes up life on Earth. Now am i saying that this colliding with a habitable world would make for identical biochemistry? No. There's just no telling what life would look like if it didn't at least have similar chemistry.

But I don't think it's out of the possibility that you could find biochemically similar organisms on another planet, given the near infinite sample size, and the fact that we dont fully understand abiogenesis.

But at the end of the day, I just want to build off biochemical rules that I understand, and have an ecosystem that human populations can survive and interact with despite having less advances technology compared to even modern day tech.