But you only introduce an unnecessary extra step in the same theory. Life still had to evolve somewhere, just that now it had to embark onto interstellar trip.
But alas, that's an external observer viewpoint. It's important to note that it does not say that life is more probable to have evolved somewhere else than Earth (since we have an effective sample size of 1). It only says that the extra step introduced in the panspermia theory does not have a negative probabilistic impact, on the contrary.
It's a big question as to why life started on Earth as soon as it did, pretty much as soon as it was even possible.
That could be because life is very easy to start if conditions are right. In which case it's quite likely to have started on early Mars too, and we should expect to find at least simple life all over the place.
The other possibility is that it didn't start on Earth, and was seeded from somewhere else.
¹Let's call them Engineers