The primary value of boards is a sanity check for the top layer of management. As an investor you want a board looking after the investors interests. You can find plenty of company's that where gutted by overly permissive boards handing out ridiculous compensation packages for example.

PS: You can compare the performance of public companies with various board makeups, it's not a meaningless topic.

The purpose of a board is to look out for owner's interests. That is not exactly the same thing as investor's interests. That is why boards aren't made up of just investors.

I never said that was their purpose, just what you want as an investor.

You can have a board focusing on balancing public good with profit, if that's what the companies charter says. But, that's probably not a great investment.

I can certainly see how investors might only want investors on the board! Screw the other owners! That would be sketchy!

You can find stations that break down like this:

  CEO and CXX of company A is on company B's board.
  CEO and CXX of company B is on company C's board.
  CEO and CXX of company C is on company A's board.

Now, no direct conflict of interest, but you can see the issue. Especially when CEO of company A also sit's on company A's board.

So, yea on it's own the co-founders on the board is not a big thing. But, looking into the board should be part of due diligence.

PS: You can also see issues when VC's make up the majority of the board, but that's less common with public companies. (Let's buy up little company X that my firm invested in.)