The vertical lift efficiency of all those small diameter/high speed rotors will be miserable. And it's VTOL operation that drives the size of the electric motors/power electronics. An electric propulsion system sized for VTOL operation that accounts for less than 5% of total flight time usually means the motors/PEs will be over-sized for the other 95% of flight time in conventional (wing-borne) operation. This weight penalty can be significant.
Compare this to
a battery-electric 2 seat rotorcraft that was actually built and flown. It was a modified S-300C helicopter which already had a well developed rotor system and lightweight airframe. The electric motor was rated at 141 kW which was the same power produced by the original Lycoming piston engine. The lithium ion battery pack weighed 1100 pounds which was limited by the S-300C max GW capability . This allowed around 15 minutes of flight with a single pilot on board.
I'm sure the engineers that designed the Firefly were competent, and the motor/controls/battery were all based on current technology. So it would be fair to use the Firefly's demonstrated performance as a baseline to evaluate concepts like Lilium.