You have a point or two there but you are also missing a point or two. Some of the drop tuning "movement" is just fadishness and it will be replaced by something, someday. But there is more to it than that. My "drop tuning" is also a fifths tuning, CGDA, like a cello but lower. Some even say that it was the intended tuning for the double bass but I think that may be assigning more intentionality to the development of the DB than existed. It seems like it was developed by many people in many places as an attempt to meet a vaguely felt need and the communication between its designers was rather loose. They were a committee who probably never met in person. And the BG was copied after that, several centuries later! Any tuning for the DB or BG that works for the musician and the music is a fine tuning. Alternate tunings for the orchestral stringed instruments are common enough that they have an Italian name for that: scordatura. Someone can double chekc my spelling of that!
I've played in this wacky tuning for several years now and I love it. Some double bassists use it too, surprisingly enough, and it was their success with it that convinced me it could be feasible on a bass guitar. Can I play in any key on a standard tuned four string bass guitar? Most definitely yes! I have in my small collection a Stratocaster variant with two strings ripped off and the remaing four tuned GDAE. That works just great in any key. The ability to play well in any key comes from the even temperment, not the number of strings or the way they are tuned.
But does having even a handful of lower than standard notes in your quiver give you more useful artistic choices? Again the answer is yes! I don't need a LOW Eb to play in key signatures that include Eb but having it gives you choices that even a hack like me can use to good artistic effect. Now the artistic utility of those lower notes is used most fully on a bass where they do not come at the expense of the higer notes which also have their artistic utility but drop (or more precisely for the bulk of this thread, LOW) tunings, even as low as BEAD, do have solid artistic merit that you should not dismiss out of hand merely becuase there are many examples of musicians who are clueless about the true value of them.
