Hi
First, I must give some credit to your expert as I agree with most of what he said.
What you are describing is a common dilemma, and indeed your chances are much higher if you have one of the three elements the expert mentioned. Companies are reluctant to pay / purchase / invest only in an idea. Additionally, even if they do show interest, you will have to expose the idea to them, at which stage they may decide to make use of it without your involvement (an NDA/confidentiality agreement can only protect you so much, and most companies won't agree to sign one).
Bottom line:
1. if you only want to sell the idea, your pitch email needs to be really good, and your NDA needs to be airtight.
2. I would consider offering that they develop it, and you get a commission in return.
3. You have a better chance if you validate the idea and collect some data. You don't have to develop the actual product in order to do this.
I've successfully helped over 300 entrepreneurs, and I'd be happy to help you with the email or in validating the product/service.
Good luck