just checked the instruction of I-140

Since i'm filing Eb1a, i always thought the following requirement is for both eb1a and eb1b. But it is actually for eb1a only.

"evidence that the alien has performed in a leading or
critical role for organizations or establishments that
have distinguished reputations,"

So maybe you are right.
But how can INDEPENDENT referees know all your information. I still think you need at least 2 people you worked with. For employer based, I think it's unreseaonble that your boss or CEO for small company doesn't provide such a letter for you.

Just my opinion.