This is fair, but they are developing a pretty compelling picture of LUCA based on genealogical evidence. It's an estimation, but it's not like it was summoned out of the ether. It's based on highly detailed and well-reasoned arguments.
As for developing estimates of probability simply because we understand how the chemistry of an environment tends to evolve from starter material (provided by a star) and known chemical reactions...yeah, I don't get that. And it becomes impossibly vague when it comes to developing estimates of how often that evolves into intelligence since we essentially have a grand sample size of one for that.YI'm not implying intelligent creation or anything like that. As long as