You are slightly taking me out of context, I'm not comparing the two bands - GD and JGB. I am looking at Jerry as a guitarist and Bob.
Jerry needed his solo band, it was an outlet for him free of other influence, it was him and John Kahn getting together and jamming, other musicans came and went. But he played longer solo's in his band, he often played his guitar louder and got to stretch his rhythm chops with just someone on the keys not another guitar. He needed that release, he loved it, he got out a whole ton of music and other songs he wanted to do that were areas that the Dead might not have covered. Same goes for his Grisman work and his other session stuff. Yes it was secondary to the Dead and a minor little sub-plot to the massive dead machine but still important to Jerry. For me Legion of Mary is possibly the apex of Garcia's playing, combining lead and rhythm playing in a brilliant manner.
We all know about Healy fooling around with Bob's guitar and set-up. Bob was a very important cog in the dead's wheel and I'm glad he wasn't replaced when he might have been in the late 60's(by David Nelson possibly).
I'm not disputing his contribution to the cause or his ability but he is only good in his own context. His solo bands are filled with Jerry-like lead players. I do believe that Bob's whole career came off Jerry, it was jerry's gift of time to Bob for him to devolpe that saved him from getting the chop. Truth is the buck did always stop with Jerry, he was the musical leader.
To speculate what they would have done if they never came together is a little hard to do, no can know that.
But I do agree with David Grisman when he said that without Jerry none of them would have had a career.
But I still love Bob and think he's great and never would I put down his contribution. But Jerry was such a giant(no pun intended) of man, with his ability, intelligence and intellect that he will overshadow the rest.