FFXI has had a top heavy for a while now, so instead of trying to create a more level-diverse population, SE has focused on speeding up the process of reaching lv99. Clearly the game has changed and is very different than it was 3-4 years ago, but it has been a good change for the most part.
There really are no 6-man parties, instead, majority of players solo or level up quickly in large groups. If you are adamant about experiencing the old days of FFXI, you can try the linkshell group mentioned here: http://ffxi.allakhazam.com/forum.html?forum=10&mid=13460146143345118
Obviously hearing this when thinking back on a game once enjoyed is always disappointing, but the best advice for new and returning players is to find an active linkshell. There are several, just read almost any new/returning player threads, then start up on that server. Returning? Chances are there is a similar linkshell on your server or you can always change servers if you'd like. What people tend to forget is that it wasn't the 6-man parties or difficult bcnm fights that made the game exciting, it was the players that you meet. Joining an active linkshell advances this step infinitely and you'll find a game with a much more casual* experience that can be just as enjoyable.
*I like to think the game just went through a big transition the last few years that has almost completely focused on a more casual style of play. Now that lv99 has become firmly established, I expect more relevant - casual, story, and hardcore - content will be slowly introduced along with a new expansion. No one knows what will come of FFXI, but SE still has tremendous plans for the future.