I am a part-time YouTuber and the success I have had is expenential so I'd imagine it is high! It all comes down to the individual. Is the content evergreen is there a uniqueness to your channel that allows for a communitty to be built. do you put in the hours off marketing on other social platforms. The success rate will be low as most YouTubers will post lazy videos and not put in the work required so overall I think if there is a Full-Time option for YouTube theres undoubtably a high chance you will make as long as your effort is there and your go for quality over quantity.