Singing and acting do take talent, yes. Absolutely but you also learn to be better. You get taught to be better. Experience, coaching, practice, etc. etc.
Same goes with accounting, teaching, and nursing. You need to be born with that brain wired for numbers to be any good. You need to be born with that brain wired to teach others to be any good. You need to be born with that brain for nursing (compassion) to be any good. The world is full of bad accountants, teachers, and nurses. They have all been taught the "skill" to do it but they do not have the talent to be any good nor do they have the temperament or personality.
This is not to say that one can not be good at something if they are not born with an inherent talent to do it. Practice, learning the "skill", etc will allow one to overcome those obstacles and perhaps be one of the best there is to be sure but comparing whether you can be successful in acting or accounting without being born with that "knack" doesn't ring true in my own head but it really helps.
I am not trying to say that if I practice enough I can beat Michael Phelps or a shark but that some things can be taught and some can't, it depends on the person. That's just what I think......which doesn't really matter in the end.
Luck? Hell, that plays into so much in all aspects of life.