How can you claim that Masters of War/Tangled up in Blue don't involve good singing by Dylan? Masters of War is particularly a difficult song, requiring real range. I do not think Noel or Liam could pull it off, but Dylan storms it.
What Dylan is strong at is the attitude. Have you ever tried singing along to Lou Reed? The notes are easy to get across but what's very, very difficult is the attitude (Sweet Jane for example). The same goes with Dylan. It's not a strictly "technical" thing. Neil Young, too.
Some of his stuff grates, some of it is great. Generally the less he plays the harmonica the better.
And I agree his voice has aged very badly but that happens even to "great" singers, Stevie Nicks for example.