I'd just make this an artifact with a flat casting cost that works forever - the rules fiddliness of when you use it otherwise seem painful. It's also kinda niche, and not obvious it's doing anything - so busywork with counters and deciding how much to charge it just seems like pain for not much gain.

A flat "Opponents only draw one card a turn (their draw step)" or something is much more exciting; while being functionally the same in 99% of games.

I wonder how painful this is for people playing cards like Inspiration. Annoying, to be sure. But it doesn't flat blank the card, like on Divination. I suppose some cards, like Archivist, wouldn't even be affected... but those cards are exceptions, and not the rule.