I have a thread about this, though its specifically for preventing manipulation of the system. Making Alliance only available if you have all three raids of a tier unlocked and players to meet the minimum ilvl requirement of the raid that is equal to their level (so for lvl 50-59 that'd be LotA, lvl 60-69 Void Ark, lvl 70-79 Rabanastre, lvl 80 Copied Factory) will help curb some of it but as with anything people will find a way. I can only hope Ct raids get put in a separate roulette like I also suggested because it'd be nice to take those off the table for a bit. I like getting a variety.