Bird have a known density. Drones have variable density. And since the tests thus far are done with birds I think it's unknown what happens when drone X is ingested into a turbine engine.
The other fallacy is comparing birds were have minimal control over, vs man made aircraft that should be as capable of avoidance as the current regime.
I'm more concerned about damage to the non engine areas of the aircraft, but they routinely survive 18 lb bird impacts in the wild. Even with lithium batteries being about four times denser than a bird, the weight being so much less means that the penetrating power should be less than a half that of a goose.
I'd be more concerned about a DJI Phantom type drone going through the windscreen of a light aircraft and injuring the pilot.
FAA standards require airliners be able to safely withstand a 4 lb bird strike.
By comparison, a DJI Phantom drone weighs around 2 lbs and is unlike to be flying in dense enough flocks to damage both engines.