Mad Maggie is tied for the lowest pick rate with Crypto, but pro players think she is one of the best Legends in the game. In theory, it makes sense as Legends with any type of damage-dealing abilities have such an advantage over the competition.
But Mad Maggie can be difficult to use, with a high skill ceiling, but based on the footage below, if you team her with Seer, she can be very powerful.
As you can see in the clip Seer keeps using his ability to locate and ping the enemy players on the roof, and Mad Maggie keeps using her drill to damage them while safely staying inside the building. She is able to put pressure on them, knock a player that just self-revived and even hits them when they are trying to pick each other up.
Granted, it's a pretty specific situation, but in the right hands the combination is deadly.
ImperialHal goes even further stating the best combination for World's Edge is Valk, Seer, and Maggie. That's two legends with damage-dealing abilities, and another Legend that can help locate enemies behind walls. It's a powerful combination for turtling teams like the situation from above, or aggressive teams pushing on an enemy's position.