The importance of Khalifman...and of Anand, Ponomariov, Kazimzhinov and Topalov...in being world champions during a time of crisis for FIDE...cannot be overstated.   They represent the rule of law  the functioning of the world title cycle  at a time when it was under direct attack by persons who viewed the title as private property, rather than as a sports title bestowed upon a player by a public cycle (as it had been from 1948 onward).  To say that Fischer, Kasparov or Alekhine were greater players...and therefore of more importance...overlooks this important aspect of Khalifman's title reign.   One could say that Fischer, Kasparov and Alkehine were stronger than Euwe and Smyslov, too...but that doesn't get us anywhere.   We don't rank US presidents by reputation  we list them all equally, yes?  Khalifman himself  in 1999 in interviews  said that although he was not the strongest player in the world (being 44th by rating)...he was clearly the world champion (having won the title in the open, public cycle run by FIDE).   That stand  that position  is what makes his title reign important.  BTW before anyone denigrates the "FIDE Title Champions" ...it should be noted that at least two could be considered super-GMs (Anand and Topalov), and that one (Anand) regained the title via the classical method.  Chesspride 66.19.84.2