^not necessarily, i dont think that has much to do with it, for me anyway. I think it's biological. a 220 pound dude feels more invincible than a 175 one. You feel and are stronger, bigger, all of that, it carries over to normal life even if it's mostly a potential thing (eg in a fight for survival) it means more confidence.
Nope, that's buying into standards. We may still have similarities to our cavemen ancestors, but we have evolved drastically since then from a mental perspective. Brute strength is not "survival". Mental strength is. Random example: Kendrick Lamar is a 5'6" guy who looks skinny fat. You think a guy like him has any sensations of feeling "vulnerable" or would feel more invincible if he got jacked??
If being bigger makes you feel more invincible, you are either very naive or buying into illusory standards. Your mind/soul makes you invincible.
What you are saying CAN bring you more confidence. If it's in the form of "I made this transformation and am proud of myself" then that's more a mental/spiritual thing.
If it's in the form of "I am stronger and bigger than you", that's buying into societal standards of what makes one better than another, which is an illusion. It's a big illusion, because you buy into it and it makes you feel "confident" but it's a fake confident, one belonging to a person who is actually mentally weak if they need that kind of validation to feel "invincible"
edit: BTW, no way am I saying there's anything wrong with working out and wanting to get bigger. It's about, is the desire coming from you or is it coming from society/other people's expectations. If it's coming from you, then training becomes an art form, one that is a very creative process.