At the highest level almost no one "knows" the entirety of football. That's why football clubs work in teams, with there being experts in every field. For instance there are fitness coaches, tactical coaches, motivational coaches, developmental, a manager overseeing everything, scouts, physios, etc. All with different types of expertise brought to the table.
I think it's possible for a fan to have a decent amount of insight in one field of football while being clueless in another, the same as any other person in a football club. The real money comes from being an expert in a particular field, which usually comes with study.
The staff who have extensive knowledge in multiple fields (usually managers) tend to be the ones with the most attention to detail, and thus are the most highly regarded. But that's not a common occurrence.