Like I said I remember the early days of FFXI where to get to lv 75 you had to have skill as well as know your job to a T. Unfortunately the casual gamers have taken interest in online games so to keep those players they can't make the content too difficult.

Two suggestions I would have:

1) if it hasn't been done already switch it so you can do all content as a under-sized party so that the skilled players can go into any content including the newest stuff coming out with less ppl to create the challenge they want.

2) Make a set of fights with various difficulty like;
- very easy - easy - tough - very tough
Or something like that. Yes it would be similar to the arch angels fights from FFXI but that would allow for a separation between skill levels. Also with this the gear rewards can be better, like item drops to upgrade old gear to like an ilvl 180 (based off the current ilvl cap)