This great advice isn’t always great.
Should you be 100% you? Absolutely. Know who you are, and then be that. Of course.
But you shouldn’t bring all of that to every situation. Extroverts know to stay quiet in a funeral. Introverts know when it’s time to speak up.
Seth Godin calls this being professional. He gives the example of a surgeon; a surgeon might have had a fight with their spouse in the morning, but you don’t want them bringing that part of themselves into the operating room.
Being a professional means bringing only those parts of your self that add to the situation.
This is how I think about the (sometimes) dirty word of “blend.” Choral conductors sometimes are apprehensive about using it, because there is a real risk for singers to injure themselves in attempting to “fit in” to what’s happening around them.
That’s not what blend means, though. Choral blend is about being a professional; bring those aspects of your voice that add to the ensemble’s voice. Save the rest for when they’re needed.