The problem with that most important decisions cover multiple fields. For example public health decisions are not purely medical. They have financial and economic implications. They are sometimes tied to issues of personal liberty. They operative in a framework of laws. They are often organisational and management decisions (e.g. where to build a hospital, how many ambulances to buy).

In general important decisions require many different skills.

This will also lead to the problem raised earlier of experts making decisions that suit their own interests (and biases).