I agree with you when you say ideas are actually worth something. When investors say ideas are worth nothing, execution is everything that's very self-serving. The idea wasn't theirs, so of course they want you to believe the idea is worth nothing. Also, the suggestion that all co-founders should start with equal shares, regardless of how much work they put in and whose idea it was, this is also very self-serving. This just makes it easier for the investors to boot one of the founders if needed, and does not serve any other purpose. This video should be taken with a grain of salt.