With the amount of new players as well as the bigger servers that are coming, I think it's time to again look at how the low level experience can be improved.
There has been a lot of discussions on how low level stuff should work, stuff like if level syncing should take away skills or not. However I think this problem would be solved simply if getting down synced didn't feel so horrible. One of the biggest ones is AOE. EVERYONE should have at least one AOE skill by Sastasha, like come on DRG gets its first at level 40?! And speaking of Sastasha, everyone should also by then at least have some form of a 1-2-3 combo. I will keep using DRG as an example because its my most played class. At level 15 they have 4 class skills, one being a buff and another a ranged ability. I would sneak in Full Thrust somewhere before that and just give Doom Spike at level 15.
Next, that wonderful line of "Trust me the job gets better at level 50". Some classes before that point don't even have their core mechanic by then. DRG gets Blood of the Dragon at 54, so any ARR content can say bye bye to that. I believe that instead these core mechanics should be given, when you get your soul stone. This is something that works well, to some extent, on some classes, like BRD gets its first song or NIN gets its first gang sign. These two I would still change, like give them instead of one song, two instead, or two gang signs instead of one.
And for these level 30 changes, how about a special mission where you actually get to learn how to use your core mechanic? Just something really simple like "Keep Blood of the Dragon up for 90 seconds". Just enough that you can get familiar with it.
I do believe that the best way to solve a lot of slow feeling combat that new players feel would be to move some of the later skills down. And changing it so that things line up over all the jobs, like every DPS gets their AOE at level 15, every healer gets an oGcD heal at this level and every tank gets a gap closer at this level.