I need a word which means capable, confident, legitimate.
It should imply no negative connotation when used in this sentence:
He wanted to become a (more) ____ accountant.
“Legitimate” would not work, because it implies that he was not legitimate before.
It needs to imply that he was a working accountant before, but became more capable. A phrase may also work, but the primary focus is to find a single word that describes this.