But the claim is that it very probably occurred and did so by the application of natural selection to genetic variation across generations over time. No specific pathway is needed. If John, who lives in California, is seen driving his car in New York with an extra 3000 miles on its odometer, we can surmise that his car "evolved" from the West to the East Coast without specifying the route, just the mechanism - he drove.
You seem to think that the possibility of irreducible complexity appearing in nature is an impediment to the theory. It's not. Possible is not good enough, just as it wasn't when the ID people looked for it. You need actual. You need to find it.
I read this from you earlier: "How can you possibly know that? nobody understand genetics to such level to make those assertions." Does that not apply to your assertions, like the one above and below? You don't know what an insuperable barrier would look like. Here you are about to propose one, beginning with "We NEVER have ..." As you said, you can't know that.
You remind me of the problem with carbon nucleosynthesis, also once thought to contain an insurmountable barrier:
"Stars produce carbon through the
triple-alpha process, where three alpha particles (helium nuclei) collide and fuse within a tiny fraction of a second. This process is so unlikely that for many years astrophysicists were at a loss to explain how carbon and heavier elements could be created in the universe. In 1953 renowned astronomer Sir Fred Hoyle suggested a solution to the conundrum: a previously unknown excited state of carbon, very close to the energy of the triple alpha process. This excited state, now known as the Hoyle state, and would act as a stepping stone to producing stable carbon."
@shunyadragon posted about synonymous mutations in base pairs not being as neutral as was assumed. Look at your comment again in the light of that. These "neutral" states might actually facilitate changes the way the Hoyle state facilitates an otherwise unlikely to impossible change from three separate lithium nuclei to one carbon nucleus.