I was thinking about what I would do if I had the chance to be the champion of magic and I think I would go to different schools in different worlds to get as many degrees as possible and at the same time I would study absolutely all magic cleaning. As if there was a cleaning spell of different intensity depending on what you are cleaning, the materials of the object, whether it is magical or not...
I was trying to get degrees because not being a good magician as a magic champion would suck but I really think my favorite magic would be household magic. Cooking food, doing laundry, cleaning the floor, washing dishes, repairing broken things, maintaining healthy plants... It would be really practical and so much faster. So, a Billy who specializes in domestic magic. He can live in a healthier environment, fixing up a place and cleaning won't take so long and he could quickly move on to something else and he could help people differently.
He could become a member of the housekeeping staff for an odd job, helping people at the soup kitchen by using magic to freshen up the appearance and durability of a garment. The homeless could have better hygiene and it would be a great help during clean-up efforts after destructive missions.
Just a specialization that seems simple but requires real effort and which highlights things that people tend to neglect or associate with less rewarding professions. A Captain Marvel who is really skilled with magic and picks out a few things he could use as Billy.
It's just there like BAM magic disinfectant, remember to hydrate yourself, separate white from black.
Billy Batson BAMF but she's just a mother from a poor single parent family