Using just the middle pup in single coil mode is definetly limiting tonal possibilities for sure.
The beauty of having a guitar set up like Garcia's is the sheer tonal posssibilities that are now possiibe with the guitar. I tiigerized my LP DC and changed it from a one-trick pony that I didn't even like very much into a guitar with almost unlimited tonal possibilities.
Garcia's set up has everything from a strat to a LP and way more in between.
If you check out that other thread that is linked in this thread you'll see waldo's 'tutorial' if you will, on when Jerry used other pup configurations, which was fairly often. Cumberland he uses the bridge pup, whhich make sense, get a little more twang. He also used the in between bridge and middle combo for estimated, which I fouund very interesting. That's actually my second favorite position, bridge and middle blended. I actually have an SDS-1 in my middle, which I LOVE, and then i'll switch to the bridge/middle and it gives an awesome tone. Then often i'll put it on hhumbucker mode so i'm using middle single coil combined with bridge humbucker and it sounds awesome.
Garcia's guitar set up was genius if you think about it,, he wasn't stuck with a LP or a strat, he really had both in one, bestt of both worlds.
SO definitely experiment with the other settings on your guitar, I bet you'll be pleasantly surprised at the amount of tonal possibiliies lie within a jerry-fied guitar. I was absolutely floored at the range of tones that my LP possessed once I got it back from being modded. Went from a guitar that just sat in it's caase untouuched for almost 2 years to my #1 guitar overnight, and it's still my favorite guitar that I've ever played. I've never played anyone's custom tiger or wollf replicas but I'm ddying to play a Moriarrty, I have a feeling one of those is gonna school my LP-tiger.