I think this idea would be more credible if we had evidence that the earliest organisms were quite complex, with sophisticated metabolic pathways. That would be

I think this idea would be more credible if we had evidence that the earliest organisms were quite complex, with sophisticated metabolic pathways. That would be highly unlikely to evolve in a single step. As it is, it seems like early life on Earth developed from extremely simple roots. That doesn't exclude panspermia, but it means IMHO we have no compelling evidence for it and that even if it's true the organism that seeded Earth was probably very primitive.