I've been hearing that VISA application can be refused... Are these supporting documents enough for the VISA to be granted?
That's correct. Even if all of your paperwork is in order legitimate, the consul can still refuse your visa for a whole bunch of reasons. For example, if they believe you might be a security risk or are not convinced that you will return to your country of origin when your visa expires.
whats the percentage of granting/rejecting the VISA in this case?
It's greater than zero. How much is anybody's guess. Averages and probabilities are of little utility in deciding particular cases. This isn't a lottery.
Bottom line: don't quit your current job until you get your visa.