To start with, I have never seen anyone come up with a declaration about the probability of life taking that route as opposed to other proposed explanations for how species came about, how variation in nature came about.
Certainly there could be other streams for life to have taken, as a matter of random chance events. If there aren't then the implications of that, alone, are striking.
I am, though, pretty unconvinced that there is any such thing as natural selection, I think the most probable explanation of it lies in habits of thought which Darwin and Wallace were enculturated into by their having grown up in the wretchedly class saturated, poor-hating hierarchy advancing Great Britain. I think it's worth noting that the proposed earlier inventors of natural selection such as James Hutton, William Charles Wells, and Edward Blyth were, as well, British. I think it is a habit of thought born of people who were advantaged by the very artificial British class system and easily adopted as such by the men and, to a lesser extent, women of that class with their attitudes towards the underclass - the very upper class who ran science and academia and publishing and pretty much everything necessary to promote the British class system as a law of nature.
I would love to see some serious consideration given to a question that has come to interest me more as I've thought about it, how natural selection as an explanation of how things developed as they are now as compared to random chance, itself. Stephen Jay Gould liked to talk about something similar as contingency but he and some others didn't subject natural selection to a test of improbabilities that I've ever found. Even if I believed that natural selection were a real thing instead of a conventionally adopted framing, imposed and maintained largely by convention, ideology and coercion, I would doubt that it as an explanation of why individuals left no or fewer or more offspring (especially based on many of the things artificially isolated so as to be called "traits" for it to work on) would achieve anything like 100% probability in explanatory power. I doubt it would achieve a 1% probability in most cases, if such an estimate could be made. I suspect its probability would be far, far lower than that. In which case, other factors must have been at work in the result that happened, immediately and through time.
One of the Founding Idiocies of Abiogenisis
Specifically, I got a violent objection to this statement:
There is no way for a scientist to demonstrate that those could have formed in that way because every experiment that could be done to prop up a materialist fabulistic narrative of that would be the result of intelligent design. You can't disprove intelligent design through conducting intelligently designed experiments.