"Drone" is a great episode. It reminds me a little bit of the episode "I, Borg" from TNG. "Drone" is probably my most watched episode from that season and definitely in my Top 10.
As for One being able to destroy the sphere...come on, he's a 29th century hybrid Borg!
I don't think the Borg found Voyager much of a threat or worthy of a long chase. The reason One allowed himself to die was because he knew the Borg would only chase Voyager down to assimilate him since he was so special and advanced.