I think you're not understanding the mechanics of how this works. At a DC 27, the only characters who has a chance of passing are fighters and paladins. Even then at level 20, they have a 75% chance at failure. Even if you house rule and say a natural 20 is an automatic success, that's only brings everyone else from a 0% to 5% chance of succeeding. So that means there is a huge chance that 100% of the party will be blinded for the remainder of the fight.
To cure blindness it takes a GREATER RESTORATION spell, which is a 5th level spell. A cleric has only 3 slots of 5th, 2 slots of 6th, 2 of 7th, and so on. They do not want to waste all of their high level slots on casting greater restoration o. The party when they can all be blinded again the next round.
Next issue is, it does damage AND blind the characters for the entire fight. Yes 1 min is the entire fight. This could be fine if it's a 1/day ability, but it's rechargeable, which means on good rolls he can spam the ability every round until everyone is blind (which takes maybe 2 or 3). The next problem is, even if the fighter makes his save, he is still blind for 1 round, which is also a problem, because he can't hit his target, unless he has a magic item that gives him blindsight or tremorsense. At a 50% recharge rate, if it was damage plus blind for 1 round would be fair on a fail and half damage and no blind on a pass would be fair.