Think the best way to summarize the difference between Jonty and everybody else is that while most players get to balls that are within their 'diving arc', Jonty could cover the entire stretch of land between Gully and cover by fielding at Point. As HB has said, this is because his anticipation and speed across the field was remarkable.
Symonds does come close, in the sense that Rhodes wasn't as good in certain other fielding positions like the slips, but Rhodes was so far ahead of everyone else in the covers that it doesnt make a difference IMO. He was comfortably saving 10-15 runs a game even if he wasnt taking a catch. Think people need to look at Rhodes pre 1999 too to really gauge how good he was, he lost a yard or two after that.
Gibbs on the other hand is far from being a great fielder IMO. He was very good perhaps, but there is daylight between him and Ponting/Symonds