8 plasma guns if they are close range is 16 shots 11 hits 9 wounds, if they overcharge you would need 7 drones to tank all the wounds as would get no save.
Or even your normal Commander usually has 2 drones if 100 conscripts shoot at long range it'll still be 33 hits 11 wounds usually 3-4 failed saves strips your drones and does a wound or 2.
The amount of rapid fire weapons guard can muster will make them top character snipers even with drones
Lets not blow this out of proportion. First of all, Veterans are only capable of carrying up to 3 Plasma Guns. Special Weapons teams are also only capable of 3 special weapons. Command Squads are capable of taking 4, but are limited to 1 per Officer.
So the worst case scenario is the Command Squad. They are BS 3+ so hit 66% of the time with 2 shots each. So 5.28 rounding up to 6 because we are talking worst case. Cadre Fireblades are T3, so wounding on 2s so 83% comes out to 5 wounds. Bounce them all to drones, drones get a 5+ Shield Gen save, so that means 33% get bounced. So after that 3.3 are not saved, so 4. 4 popped Shield Drones. I am not worried about 4 popped drones, especially when they could have done the same thing with First Rank Fire, Second Rank Fire into my Fire Warriors. Either way, they are only killing drones, and not reducing my killing capacity in the slightest.
Is it a nice tactical order. Yes. Is it something I wish we had. Yes! Do I think it will see use. Yes. But remember it shares a limited pool of available Orders per turn with some other very impressive Orders. Its a nice tool to put in their toolbox, and it will win or lose some games, but it does not sound like it is excessive or game breaking.