first, of all, I'm not defending the O-PGL 79 CD. I'm just trying to make a point that it is so easy to say "oh nerf this it's broken" but in reality, a "clear" nerf could ruin a weapon and we would have a bunch of norsmen in the game, a weapon that is just there and is not being used.
For example, the nerf that you suggest is quite radical. Reducing the range with 30-40% would make it A LOT harder to do anything the O-PGL 79 CD.
It would reduce the explosion range from 1,000cm (10 m) to 700-600 (7-6m) and that's just the range for the minimum damage. The area for the max damage would be around 60 cm. The final effect of this would be that the average user would go from 2 nades to stun to about 3-4 nades to stun.
This would make it useless.