Oh god, Asta. Nah, it's not actually that bad. My only problem with him is his ability. Absolute Magic Nullification is, in my opinion, a bit too much and hasn't done anything but take the tension out of his fights. The idea behind it is fine, but the execution leaves a lot to be desired.
The author probably could've played up the demon angle and had it where Asta's sword "eats" magic. It would allow Asta's sword to drain magic and weaken it, but it would also mean that those who have higher reserves of Magic wouldn't be completely useless as soon as the sword touches them.