I know one problem that is cropping up is that the level gap is really starting to hit some people hard.
My wife and I just hit all jobs to 50, and I would say that 90% of our linkshell only has 1-3 jobs to 50... (point is, if we are at 50, there are a lot of others like us... we weren't the fastest levelers, but we are now disqualified from leveling with people below ~40).
What ends up happening is that 1-3 people in our linkshell decide to exp. Of those people maybe 1 person has a job around their level.
Nobody learned how to pt in the game (it has always been get as many people together and ZERG-BLAST EVERYTHING). So, now you have a DD and maybe a tank or a healer (if you are lucky) looking for a party.
Camps have changed, mobs have changed, nobody is talking about what to do or where to go, or how to do it, and so they sit around looking for a full party (when you actually get less exp the more people in your party, but you can kill faster, making it potentially just as effective to fight with 2 people as it is with 8). Combine that with people Powerleveling through most of the low levels...
At the end of the day, yeah, Mysidia is a pretty busy server all things considered... But finding 8 people level 1-10, 10-15, 15-20, 20-25, 25-30, 30-35, 35-40, or 40-45 is INCREDIBLY hard.
I mean, simple math, you have say, 600 people online. You have 9 level ranges to work from (including 45-50, which is where most people are available).
Just having a single party at any of those given level ranges would eat up nearly 100 people. Then take into consideration the time it takes a party of that size to level (you can go through any of the first 5 level brackets in less than an evening, in a good run, you can make it through all 5). Meaning that if you found a party, that same party would out level you in a blink of an eye if you had to go. It's not like it was in 11 where people level so slowly that you can run into the same people with the same job regularly day after day.
It would easily take 1,000-3,000 users to make it so that it would be easy to find parties. Considering in 11, there was never a time when I was playing that the userbase was below 3k active users, and I had several hours of not finding a party.
For people who are sticking it out. Try and get a party of 2-4 people going. You might be amazed at how well things still go.
Leves are also not a bad thing (tedious, and time consuming bouncing back and forth between town and crystals, but the exp and rewards are nice).
But with a healer and/or tank, and/or DDs, you can have a party that still exps quite well together.