obviously it is not unique to FFXI, but its one of the only MMO's i have played, so i can't speak on a game i have never played
if soloing was possible to do in a reasonable timeframe in ffxi i would have done it too. i leveled melee jobs, the everyone-and-their-mother-played melee jobs, so i deffinitely know about the shitty aspects of party play in ffxi and by no means am calling it perfect lol. im just bringing it up so as to better speculate on how FFXIV can improve on this.
maybe they could implement places to level for any size party. for instance, can't find 6 ppl to go kill raptor parties? grab 1 person and go to a place suitable for 2 man parties. i think something like that would help alleviate the wait time for those who want to party, without forcing them to have to wait for the right classes to pop up.
i dont think it would be a great idea to make it so that you can solo all the way to endgame, because then when you get to endgame and you start participating in large-scale battles, you wont have a clue whats going on or how to work well with other classes for the most part(ever done a pick-up raid in WoW? then you know what i mean lol). i for one think endgame should be an area of the game for pro and dedicated players.
i like what they are doing with guildleves, and i wonder how great the differences in rewards is when completing them with more people. it should be a considerable difference, so as to encourage, not force group play. i speculate that that is the key to this games success.