There was already topic about this on dungeons forums, but it was written in so broken english that it was barely understandable.
Levelling instaces have lvl sync so they cant be facerolled/carried by high lvl chars. So why there is nothing like that for end game content? As the progression becomes gear-based, the sync should be by average item level. Generally, the max avg item level should be equal to the level of items dropped in instance, for example:
WP - max average ilvl 55
AK - max ilvl 60
Ifrit - 60
Garuda - 70
Titan - 70
CT - 80
Coil - 90 (this will be imortant once higher ilvl gear appears), however separate can be considered (t1 - 80, t2 - 83, t4 - 87, t5 - 90)

This way crystal tower and other new instances wont be facerolled by ppl overgeared so much that they wont have to pay attention to mechanics. Also instances will retain some of their challenge. No more titan carries without effort of the carried one. No more "lfm ak/wp sr relic + 1 full dl only". They have the same power as less geared player. No more having to gear up alt job with main job to the point of making playing that job pointless.

However, it may change to "lfm ak/wp sr only full penta melded gear". In order to prevent that, the average ilvl sync should be based per attribute bonus. A particular instance will have caps of:
1. Weapon phys/magic damage cap. Based on job.
2. Gear phys defense cap. Based on role, but separate for phys/magic dps.
3. Gear magic defense cap. Based on role, but separate for phys/magic dps.
4. Shield block cap.
5. Primary attribute cap (str, int, dex, mind)
6. Vitality cap.
7. Combined secondary attribute cap. A weighted sum of acc, det, skill speed, spell speed, crit, dex for tanks, parry and piety.