alt Hacker NewsKuala Lumpur gets (generous assumption) about 100 lightning strikes per square kilometer per year [0].
If a single drone could service a lot of square km, then it could conceivably collect a lot of electricity. E.g. if it could service 20 square km: 20 * 100 * 8mWh = 16gWh per year. Not bad, but an upper bound, and it hinges a lot on that first parameter (service area).
You need ~4 strikes per hour to keep up with a single large offshore wind turbine (15MW at 40% capacity factor).
That would mean 350km² just to match a single wind turbine (at 100% capture efficiency for 5GJ lightning strikes).
This is not ever gonna make economical sense.