Between Gamma Jack and Gazerbeam, I believe Jack is easier to write as a villain than Simon because he already held warped beliefs. He thought Supers were a “superior race” because they possessed powers, and he had a history of killing criminals. The NSA placed Gamma Jack under A-level monitoring because his personality and behavior made them fear that he would become a villain. Jack could become a villain because of his superiority complex, viewing powerless people as pathetic weaklings beneath him, or because he seeks revenge against the NSA for personal reasons. Because he held himself in such high regard, he would most likely work alone or form short-term partnerships.
As for Gazerbeam, it’s harder to formulate why he would become a villain in the first place. Maybe he would become disillusioned with the justice system or believe Supers cause more harm than good, viewing them as a plague on society. In terms of personality, others regarded him as aloof and boring, finding him off-putting, which caused conflicts during his time with the Phantasmics, Phylange, and Apogee. Considering Simon’s difficulty forming relationships with others, he would’ve stayed alone if Bob, Lucius, and Jack hadn’t befriended him. As a villain, he would mostly act as a lone wolf and avoid getting too close to anyone in fear of his identity being revealed.
Jack is easier to write as a villain than Simon because he already had a problematic mindset and troublesome tendencies, whereas Simon does not. You would have to give Simon new qualities that still remain quite in character for him to work as a villain.
