But it isn't just the rate of reactions you are interested in. It is the conditions that led to these reactions in the first place.
So you look in the universe that we can see, the abundance of organics in molecular clouds is well known and they are well distributed in our galaxy. The goal of science is approximate models, never exacting recreation.
That is why people who are careful use terms like 'seems likely' rather than 'it happened this way.'
Your criticism would strip away almost all of astronomy and physics in one fell swoop. We can’t know anything about the conditions in the past, we can only theorize and draw some tentative conclusions from the evidence.
It still seems likelier than not the earth’s moon was formed in a huge collision.
Where did the earth come from, what was it like, where did the impactor comes from, what was it like? We will never know, it is still a very valid theory.