What makes you think that these drones are made in Iran and were simply renamed Geran-2? Do you have any proof of this other than allegations?
C'mon, even advisor of Russian Defense Ministry said that these drones are made in Iran, but they can't talk about it because they offcially don't recognize that they're made in Iran:https://www.youtube.com/watch?v=PZsrQE9fIjE
Here you are wishful thinking. These drones are extremely difficult targets for an air defense system for a number of reasons (they fly at low altitude, their body is radio-transparent, their fuel tanks are reinforced, the air-cooled engine is cold). Plus, it has a contact-type detonator, that is, even if the drone was shot down, it will still explode when it falls. And perhaps the damage from a downed drone will be even greater than if it is not touched.
And somehow they managed to shoot it down with good old Buk 1M:https://www.youtube.com/watch?v=b9LvhqlO2Rs
If these 80% would be just wishful thinking, consquences would be much worse.
Attempts to shoot down Geran-2 from an aircraft have already led to the loss of at least one MiG-29 of the Ukrainian Air Force. The Stinger MANPADS guidance system does not see Geran-2 due to the cold air-cooled engine. Any small-sized low-flying target is a deliberately difficult target for air defense. Don't talk to me about the 80% downed drones when there are rolling blackouts all over Ukraine.