> if it did I would have thought it would have appeared in the past 5 billion years or so

It may have appeared and been outcompeted. That doesn’t suggest its (artificial) reintroduction would again be outcompeted

It does actually, because it implies it fought and lost that battle the first time.

Now, with L-amino life everywhere it would have an even bigger starting problem.

We see this with extremophiles: organisms which can grow in nuclear cooling ponds full extremely badly when transplanted to nutrient rich environments with other, less capable organisms.