Yea, the multiple Darths throughout the PT did get kinda lame and it's almost as if it was there just so Lucas could conveniently work his way From Darth Maul and Darth Sidious (and the backstory of Darth Bane) in TPM to Darth Tyrannus in AOTC to the backstory of Darth Plaguis to Anakin being dubbed Darth Vader by the emperor in ROTS. Correct me if I'm wrong, but whether or not it was implied that Vader wasn't the only Darth, he was the only Darth we knew about until TPM was made. I didn't like finding out that the Emperor was also a Darth. There was one Darth too many in TPM.