The skill up system is outdated.
At 75 back oh so long ago, generally you would be able to skill up your main weapon or magic in the time it took you to go from one level to the next. It worked very well for keeping your main weapon capped, and maybe doing a few levels of a side weapon, when you needed a skill up party it was usually to do an entirely new weapon, but otherwise you were never truly lagging behind on the main skills you needed.
Now roll on Abyssea exp / Grounds of Valor exp / general changes to exp caps etc and you go from leveling up in parties which make 10k-15k exp per hour, to alliances which are making 150k-350k exp per hour, and this is brilliant, I love that the boring grind to get a job to the max has been replaced with something more quicker and relaxing.
However the current skill up system was not meant to deal with this. For the longest time I've avoided leveling any job I dont have skills already for, but recently I gave up and picked up BLM, having never leveled any other mage job besides BLU, so a lack of all magic skills here. After a weeks work I ended up 90+ BLM, but with around 200~ Elemental magic skill, and 140~ enfeebling magic skill, I tried to keep them up... but the gap of your skills gets wider and wider no matter how hard you try while exping.
I picked up some magic skill up foods, went into abyssea, and sat for an hour or so spamming T1 nukes on decent challenge monsters, in total I got around 10 full skill levels, for an hour of work, with food which on Asura costs 100k-300k a stack depending which type you pick up, great 230 more skills to go. And considering the majority of skill ups gets increasingly harder to cap the closer you approach the cap, well this would probably work out to more time spent skilling up then it took to level the job. Which frankly, shouldnt really be that way.
So what I'm suggesting is that the skill up system should be looked into, as I doubt anyone enjoys spending countless hours in Abyssea spamming spells on mobs, gathering up 10+ mobs and leveling up your combat skills by retaliation on WAR, or what the majority of players seem to do - use some 3rd party script and AFK over night for enhancing / summoning. Expensive skill up foods (which get no official explanation for which to use when) and extremely rare skill up equipment don't really cut it.
My suggestions? Besides just plain increasing the rate of skill ups by a hefty amount, I would suggest that people can put merits into their skills in a different way, I have 30 merits sitting doing absolutely nothing, I gained them through exping (how we should be skilling up), why can't I use 30 merits to increase my base skill of a magic / weapon / defense as well as the total cap, for example putting those 30 merits into Elemental Magic and raise my current total skill to 230~
Anyway, rant over! Back to spamming Stone on mobs.