What do you know? What can you do? What do you need to learn? What do you need to practice, to improve? The greatness of a singer is somewhat analogous to the greatness of an architect. Singers will only be as good as what they know and what they can do with what they know. Many singers fall short with musicianship. They cannot name or identify what they have heard as far as chords, chord progressions, chord voicings. Some can, though. Ear training, as it is called, can enhance such skills. Music theory is also helpful. There's much more, though. Here are the 18 Components of Singing Mastery: How would you estimate your level regarding these?
1.State of mind
3.Goal setting and achievement
9.Vocal Use (Technique)
14.Business and Financial Expertise
Architects know about function and structure and forces of nature and chemistry and physics and strengths of materials and environmental control systems and human needs and code requirements and much more. You might think a person who draws plans and doesn't think much about it is an architect. There is as much skill and knowledge to every art. Some things are definable and some are not.
Musicianship is a vast subject and so is vocal technique. Many singers have the talent but lack elsewhere. Sadly enough, some are in a very bad state of mind which can and will affect the art of singing or music. A singer with no charisma is a very sad state in that it is also a state of being blind to objectivity. There is so much more than meets the eye, with being a professional level performer. Some people do sing just for fun and that's okay but the chasm between that at successfully performing is deep and wide, only to be bridged by enhancing the 18 components of singing mastery.