You are both stretching the definition of "good scientific evidence" as well as completely misunderstanding the very nature of the science producing those studies.
First, are you saying that whatever "differences in risk preference" found (for some definition of "good level evidence": I haven't seen the studies, but I'm sure they weren't done on, say, a sample of a ten-thousand people) account for the huge difference seen in SV startups? I mean, I don't know what the effect size was in the studies you were referring to, but I'm sure it was nowhere near that we see in SV.
I call such an attitude "sciency" -- ascribing small-n studies with low effect size the scientific rigor of proof or strong evidence to reinforce existing biases. You will never seriously consider this level of evidence "good" if something important to you depended on it.
Second, and much more importantly: even pretending those studies were conducted on a billion people and showed a 5x difference (or whatever it is among SV entrepreneurs), all it means is that this is how people behave now.
Sociology doesn't purport to be physics, and those aren't laws of nature. I mean, you could have done literacy studies in the 1800s and shown that blacks are illiterate (with much more statistical rigor, BTW); what does that mean? You must remember that sociology (and often psychology) studies snapshots of society that are a result of forces that we have the power to change (and probably the moral obligation to). Sociology studies things so that we could change them. It doesn't claim (in fact, it claims the opposite) to uncover fixed laws of nature.