Why did anyone think that a 4-C could beat a High 3-A when they both have similar hax?
Also, a serious problem with these Bill vs Discord debates is just their general demeanor and how they go about using their powers, Discord uses his powers to be fun, silly, and chaotic, while Bill uses his powers to be creepy, demented, and weird. Just in general the way Bill uses his powers makes them more combat-oriented than Discord, who has technically never actually fought anyone in the series, he always just messes with them for awhile and then gets turned to stone.
Basically even if they were equal in terms of power, Bill would still stomp just due to their differing personalities and motivations.