I think it's actually the opposite: if there's a good founder/investor relationship, the investor is an extended part of the team, is sometimes on the field (helping close job candidates or doing customer intros), and is often trying to help from the side-lines. Not all founder/investor relationships are this good, but some are.
To use your analogy, the founders are football players, and investors are somewhere between "football fan" and "football coach", but probably a lot closer to coach than fan. It's true that neither coaches nor fans are actually on the field playing the game, but coaches have way more insider info. For example, they watch players practice and have a deeper understanding of what each player can and cannot do, they know which players might be nursing injuries, how to motivate different types of players, etc. That doesn't mean a great coach could be a great quarterback, but I think lots of players would agree that a great coach knows a lot about how to become a better football player despite not being a football player themselves. (And to extend the analogy, I think coaches are good at helping players improve despite the fact that some players might lie or make excuses or paint rosy pictures or whatever.)