Before I get into this I don't think Sugar was the worst character ever she was somewhat amusing but she didn't work as an antagonist for several reasons that I will explain
Reason 1: the eliminations she caused
The way she eliminated people usually had nothing to do with her and strategy. When she eliminated Ella she used her singing against her which is a good idea for her to eliminate Ella if it wasn't for the fact that Chris watches every challenge except for that one for whatever reason which is just kind of a lazy way to make Sugar more antagonistic.Then later she would eliminate Jasmine which I was more ok with it. I know the season was shorter than most other seasons but she eliminated less people than Justin a secondary antagonist.
Reason 2: there were other contestants who would've worked better
Like I mentioned befor Sugar wasn't very successful but Amy and Scarlet probably would've worked better granted Amy probably would focus on Sammy and her friends but that would give her a good reason to eliminate Jasmine, with Scarlet I think if she didn't focus on Max and go crazy I bet she could've eliminated over half as many people as Sugar but this is basically complete speculation on my part.