People DO underestimate their own abilities, and it can be very damaging to their careers and lives.
For example, I have a friend who genuinely has world-class skills in a couple of areas, but spends most of his self-talk time telling himself that he's not as good as anyone else at those things. That's done significant harm to his health, livelihood and happiness.
Telling him, as you seem to be, to just accept all those false beliefs about his inadequacy isn't going to help even a little bit.
Having said that: you do make a very valuable point. If the other people really are better than you, then it's far more valuable to acknowledge that. But it's very important to be sure you're right in your estimation of your own skill before coming to that conclusion.
Whilst it make be the case for you personally that you never underrate your own skills, that's far from universal.