Expert opinions can help policy makers be better informed on aspects, but all policy involves trade-offs.
Economists can help predict what might be the fiscal or monetary consequences of plans, education experts have things to say about how different learning environments affect those with different learning styles, firearm experts often seem needed to teach even the basics to legislators pushing control, healthcare experts can predict what health consequences may be with certain medicines or procedures or recommending actions, psychologists and social scientists can predict or diagnose what responses to things like lockdowns might be (think domestic violence rates to substance abuse to obesity), climate scientists may make some good models on climate change trends...
But our current world relies on specialization of knowledge and nobody knows how to make a pencil. For an expert in one of these fields to believe they're expert in all, most, hell... two or three... is hubris.