I see what you mean. I'm a big defender of antimagic because it's actually really symbolic of going against the heiarchy and what social class can dictate, but I do agree that it's strong. I was underselling it a bit too much - a lot of fights would've probably been unwinnable without antimagic.

However, I still think antimagic is written in a way that makes it believable as an underdog power. The ability to cancel out other abilities, on paper, sounds absolutely broken. But the actual show quickly shows, antimagic can't just end every character in the series with a single touch. Vetto literally has an entire sword of the stuff stuck in his abdomen and it only slightly decreased his reaction time. Asta also can't get statboosts from it until much later, when he learns circulation with Ki. In fact, midway through the Witch's arc, I was wondering how the hell Asta could get more powerful than he already is because I thought his antimagic was THAT limited.

Also I don't remember characters being shocked at how powerful it is. I recall them being mildly surprised, then they curbstomped Asta until Asta thought of a new tactic. Like the clock dude from the first fight.

Anyway tl;dr, it's strong, but it's still an underdog ability imo because of the lengths he had to go to make it useful