When it comes to Dragon Ball, we all know certain heroes are pushed into the spotlight far too often, Dragon Ball Super being rather egregious with it in terms of how often Goku saves the day. Villains aren't looked on as often as being wasted or underused, but that's been the case on several occasions.
In some cases, it's due to a villain getting marginalized, and in other cases, it's a noncanon character that ought to make headway into canon. The reverse is also true, certain villains overstaying their welcome for far too long.
10 Underused: Raditz
Raditz was one of the most underutilized characters in the whole series. He may not have been the strongest of Saiyans, but he was Goku's brother, a fact that feels like it was glossed over in the series since Goku didn't remember his past. That angle could have been expanded on to give his character more depth and in turn, make for a more compelling fight between him and Goku/Piccolo. Instead, he was just used as a stepping stone towards Nappa and Vegeta.
9 Overused: Frieza
No one is more overused in Dragon Ball as a villain than Frieza is. He's had a movie, a saga, and was even used as an enhancement character for Trunks arrival. The way Super is treading, it doesn't seem like he's going anywhere either, granted it may not be as a villain (despite his claims). He's used as often as he is for a good reason, as Frieza is one of the best villains they have. Him coming back in Super felt a little forced, however, introducing an old hat when they could have gone with someone new.
8 Underused: King Cold
This isn't to say that King Cold needed to be some major villain that required a saga as long as Frieza's was, but using him as filler instead of Garlic Jr would have been welcome.
He had great voice acting, sounding incredibly smug and pompous, as you'd expect from Frieza's father. Seeing him taken out without doing a single thing besides swinging Trunks sword felt like a waste. He could have been a nice way to give the other characters a little shine while Goku was away.
7 Overused: Red Ribbon Army
The Red Ribbon Army is the only villain that managed to carry over from Dragon Ball to Z, thanks to Dr. Gero. While in Z the story was more focused on the androids than anything else, it was still a carryover from a band of villains that got a very long story arc in Dragon Ball. They aren't a bad villain but suffer a little in the same sense that Frieza does. They lingered around for just a little too long and were better off being left back in the original series.
6 Underused: Baby
Most will groan and roll their eyes seeing someone from GT make it here, but Baby and more importantly, the Tuffles are an intriguing adversary that should have a greater role in canon. Having someone have a similar vendetta against the Saiyans that Vegeta has towards Frieza is a cool role flip. The way they can infect others and take over their bodies is another unique ability that was only ever touched on (except with Ginyu which was more played for laughs).
5 Overused: Vegeta
This is an aggravating aspect of Dragon Ball that really should stop. Vegeta was a great villain, there's no doubt about that, but that time has passed. He's better in the role he is now, yet, one way or another he's always the one that gets turned into being a villain.
When it happened during Buu's saga it made sense as he continued to have lingering feelings of inadequacy. Then it happened outside of canon in GT with Baby and in Super due to Commeson. Neither cases were his fault or part of his will, but rather just cheap ways to use him as a bad guy again.
4 Underused: Janemba
There's a reason that Janemba made his way into Dragonball Fighterz. He's a popular character from the movies that most fans would like to see made canon. He wouldn't even need a super long arc, just something small that let the fighters of Universe 7 deal with an array of demons with Janemba being the end boss of it all. With his lack of a personality, you wouldn't even need to make an in-depth story for him; just give an excuse to see some cool fights.
3 Overused: Androids
The use of androids in the series is even worse than the aforementioned Red Ribbon Army. They show up in just about every single series as a bad guy, even including the noncanon movies via Android 13, and GT with Super 17. Outside of the storyline in Z, where the surviving androids were turned to the side of good, none of the stories have been all that interesting either. More often than not they are just dull and emotionless entities.
2 Underused: Cooler
Cooler's inclusion here has more to do with what his interactions with Frieza would be like rather than him as a character. That isn't to take anything away from him, as he's a top tier movie villain who rightfully got two different films about him. His greater impact would be to give Frieza a rival that could help continue to push him, and even further develop him as a character since Toriyama wants to keep him around.
1 Overused: Broly
No matter how you feel about Broly, you'd have to admit four different movies about the character is beyond excessive. One of which is possibly the worst in the entire string, Bio-Broly. The character just doesn't have the level of depth needed for that much exposure. While the fourth movie was an improvement, giving him far better motivations than Kakarot crying, the fact remains that he's the most overused movie villain in the whole series.