Even if I agree with Beghelli on the indifference of voice type for being a successful singer.
Although, you have to choose the song you feel comfortable with. Do you feel at ease when you sing 'Ain't no sunshine' ? I can't decide if your not at ease or if it's the recording that give me the impression.
I advice you to project your voice more, add some volume. Sing like you had to hear distinctively heard from the other side of the room (without screaming). You can look for some exercise on youtube (not only for singers actually: teachers, actors, commercials, sellers,...).
There is plenty or alto or mezzo female singer today but I have no low male range singers in mind right now.
But the range is something you can work on, I'm sure you can actually hit Withers' pitch if you work on it.
Let us know when you upload a new sample
ps: I'm not a expert at all, I just speak with my little singer and comedian experience.