Sure, speaking is a skill. In terms of improving it, some might get more out of it than others. That's as it is with all skills. However, stuttering is a quite particular factor in that regard. If you want to talk about improving the stutter, we're talking about managing it (speech therapy). As for causes for stutter, the science isn't quite done yet, so we don't know enough. - Careful that you don't buy into mainstream tropes too much in your self-understanding. Stuff like "inherent", "genetics", "extrovert", "introvert" and "born that way" is not really helpful. It often stops people from looking further or differently at things. Instead, just try things out and see what happens. There's an effort involved in all change, so it's important to stick to it. - Instead of judging yourself through recordings, ask your friends. A recording is not the same as a social setting. - Also, stutter doesn't go away through practice of that which you mean to present. Stutter varies depending on what you're doing, and it's important to be aware of that - the actual performance in the given situation is what matters, and not rehearsal or simulation of it.