I love Bob Weir. At one time I believe he was one of the greatest rhythm guitar players in the world. Jerry would not have spent all that time playing with a slouch and Weir was definitely no slouch. Sneaky good, a lot of his music sublimely inventive in the background. Great ear.
The guy was a definite ace on the cowboy songs too. Bob was also a really fine singer in his day. But he had a habit of using a little too much volume and shouting at times and I think it may have screwed up his voicebox permanently.
I honestly have a real hard time listening to his post Grateful Dead stuff. It sounds like it hurts for him to sing. His voice has not aged particularly gracefully and he seems to labor hitting anything approaching a higher register.
Aging is a fact of life, the only organisms that don't age are already dead. Some musician's voices get whiskey sounding with time, think J.J. Cale or Prine. I don't think Bob was that lucky. Admire him for trying but just can't listen anymore.