I think what SE needs to do is make a progression. Start things out slowly, teaching you then go all the way to the other end of the spectrum where mobs will rip you apart in seconds if you screw up.

Things should remain fairly casual in terms of time requirements maby 30mins - 90mins max in this game. But I feel the difficulty should not suffer because of it. I would love a hard casual based game honestly.

The more someone advances the more difficult something should be come. Without a challenge things become dull and boring.

Rank 1-10 activities should be crazy basic and simple. Geared towards teaching people the basics. Maby even having npcs to work with players in instances where you have to make a regiment with a NPC to progress or where you incapacitate a mob. Slowly teach people the more technical parts of the game and introduce it early so they completely understand how it works later. Mainly Solo based at this point.

Rank 11-20 should start putting more pressure on the players have them focusing on more difficult task where "Running in and swinging a sword might lead to death". Start adding some group content at this point but keep it on the easy side to get people use to doing it. Start to put focus on Grouping for better outcomes, but still heavy solo focused.

Rank 21-30 start giving people the meat of the game. Put in the first dungeon more on the easy side, start having some activities which require groups to work together at this point to accomplish a goal successfully.

Rank 31-40 Give people a challenge at this point. Boss instances which require regiments and incapacitation from the group. solo activities which require knowing how your job works and the world around you.

Rank 41-49 Make this semi hard. People should know their jobs now and should be getting near the mastery point.

Rank 50 (Endgame) Make some stuff challenging, some stuff really hard, and some stuff stupid hard. Not in terms of time but in difficulty. Things should go from the difficulty of Fafnir to the difficulty of PW/AV. Yea maby not all the casuals will reach this level of skill, but removing any hardcore elements will chase away that whole playerbase.... which in FF made up the majority of XI. The best gear should not be easy to obtain, it should require skill and knowledge which even a casual with enough time can easily obtain.