I produce music. I have recorded with a lot of songs with artists. I like your voice. You can make something of your voice.
What you need the conviction in your voice. And I hear that really hold back in volume as well. Try to imagine that you need convince someone that is 100 meters away from you and can hardly hear you. And all make that some FEEL what you are trying say.
It is good to learn other people raps but there is a problem when you rap over an existing track. You will not find your own voice. You will always try to imitate the original rapper (because that is the voice you hear in head). Try and get some instrumental track. Write some own lyrics (doesn't have to be much) and rap over that. This way you will find your own voice.
Keep going. Don't let anyone talk bad about you because they only know how a finished studio track sounds like. They have no idea that Jay-Z, 50 cent, Kanye West, etc sounded just like you before they were famous.