It sounds bad to say, but there should be a separation of Casual and "hardcore" content and casual players shouldn't have immediate access or even quick access to that content. Striving for something out of reach is one of the biggest draws of an MMO, joining an MMO to play 3 hours a week shouldn't get you the same benefits in any reality.
I think it is going a little far to say that there should be separate content that people can't access. Let's compare two players in the same guild.
Let's say on average it takes...10 total runs to farm gear (8 pieces) from a few T1 instances that will put you in a position to realistically do well in a T2. Each run takes a group of organized players about 3-5 hrs to do.
Player 1 does 12 (unlucky), 1 a day - 3x a week, and has now spent about 60hrs over 4wks getting gear. It's the fastest most efficient way to hit the goal amd Player 1 is able to block off those 3-5hrs at a time to get it done. Let's go ahead and include prep time of 1hr per run. Total of ~72hrs over 4 weeks (let's call that a month). Player 1 spent, on average, around 18hrs/week or just over 2.5hrs a day playing the game to achieve this goal. Bam. Player 1 is hardcore - Player 1 @#%^ing rocks.
Player 2 logs in 3x a week and one night during the weekend. Most of the time they can get on for 1-2hrs and on the weekend night can sometimes marathon for around 5hrs, average 3. They can only manage a single T1 instance run a month. Player 2 plays an average of around 7hrs/week or 1hr/day. However, to get 8 pieces that's 10 runs at 1 run a month if they're lucky. Should it take Player 2, who is playing half as much on average as Player 1, 10x as long to achieve the same goal?
Instead, Player 2 should have other options. Escorts, outpost defense, survival, etc...P2 can do this stuff in the limited time they are usually on. The rewards (GC Seals for FFXIV) allow them to get a piece, that isn't quite the T1 set but certainly good enough for the T2 instance, once every 1-2 weeks (depending on difficulty attempted, success rates and luck). So now, instead of waiting a damn near a year (and possibly losing interest due to lack of things to do) for their 8 pieces of gear, player 2 can gear up and run the T2 in a little under 3 months if they get lucky on the couple raids they can manage to run in the 12 week span.
2-3x as long seems way more reasonable than 10x as long. Especially considering the player is playing about half as much. As long as the goal is attainable and in a reasonable amount of time people will continue to play instead of saying, "@#%^ this. I'll never get to participate in endgame." and canceling...