If you want to attain excellence in public speaking, it is possible. But you must be ready to do what is necessary – practice and practice. It is through practice that excellence is attained. I know a great actor who attributes his great ability in performing arts to practice. When he was young he used to perform in front of imaginary audiences. At the end of each performance he would get imaginary feedback from imaginary members of his imaginary audience to help him improve.
Many stars use this method to perfect their skills in their chosen field. Take star footballers for instance, they would get on to the pitch and practice playing football with only an imaginary football. By doing this over and over, they would become excellent.
You can adopt this method if you want to be a great speaker. Practice talking in front of an imaginary audience. Talk as if you were delivering a real speech. Have it recorded so that you can listen to it yourself and make corrections. If you keep doing this, you may eventually become the great speaker that you aspire to be.