The board can and should be friendly with the p-corp owner. Almost all the time they are going to be green light everything. They are really just a "sanity check" (literally).

Now you could say how do we "make sure" the board acts when the time comes? Stands up to the owner? Maybe we don't. We put the mechanism in place, and if the board fails to stop the owner, then it didn't work in that specific case. And the world will know that. But as long as it works "most" of the time maybe that's enough.

Also I forgot, apart from a board a big thing might be reporting. Your p-corp activities would have much more stringent reporting requirements compared to a private individual. You can do anything you want with your $300M in private funds, including get it as small bills and roll around in it, but the p-corp funds need to be much more closely monitored. That alone, even without a board, would be big.