Hello Mefisto: This is an interesting post to me. Thanks for sharing it. You & I have some things in common, but for quite different reasons. I have also always lacked confidence, been insecure, & emotionally vulnerable, although growing up I did have both my father & mother. I was an only child. (I should also mention, I'm older now.) I have never been much of a leader either, although there were times I would like to have been. There have also been times I tried. However, I'm not a follower either. I'm now more of a non-participant. I pretty-much just keep to myself as much as possible.
The other thing that sets me apart from you is I am transgender. I've always lived a fairly typical male life. But "inside", as we say, I always felt I should have been born female. Still, I never really thought of myself as being particularly feminine outwardly... certainly not masculine... but not feminine either. Just sort-of neutral. However, during one appointment with my last therapist, she once stated: "You know, you do not have the most masculine walk." This had never occurred to me previously. Hearing this though caused me to wonder if this may have been part of what tipped all of the school bullies off growing up. I ran for my life all the way through high school. I'm still not a male who would be of much help in a fight. However, at this stage in my life, I would not be expected to be either. So this no longer is of much significance to me.
So, with regard to your questions, from my perspective, I would say that the answers are both yes & no. I believe your T is probably correct in one sense. If you're inherently a "beta", you can probably never be an "alpha". This, from my perspective, is a matter of genetics. There are limits to change. Some things are just so ingrained in our make-up that trying to change them significantly is a recipe for lifelong unhappiness.
This does NOT, however, mean you cannot grow & become confident & develop leadership capabilities. Confidence is built upon success. And you can learn to create stings of successes for yourself, building from the simple to the more complex. And each time you succeed, you'll gain confidence. Leadership skills, by the same token, are frequently taught, and can be learned. There are may different kinds of leaders & not all are alpha males. In fact, I would suggest that some of the better leadership styles are probably beyond the capabilities of most alpha males.
One important aspect of leadership, from my perspective, is expertise. If you develop expertise in a given field, people will naturally seek you out & look to you for guidance. No one is a leader everywhere & with regard to everything. And a person who tries (probably an alpha male) will simply come to be seen as a loud-mouth & a bore for the most part. However, within a given field, it is certainly possible, I believe, for a very beta type person to develop a high degree of expertise & to come to be viewed as a leader in that field. Does that make sense?
Your T was wrong about one thing, as far as I'm concerned. You do not have a "role". There is no "role" for you to get used to. You create your own destiny by your actions, or lack thereof. Perhaps it's true you cannot become an alpha male. (From my perspective, why would you want to?) But you can be highly successful & a leader within your chosen field if such is what you want & you put forth the effort to make it happen. My best wishes to you.