ESRB ratings aren't about whether a child is able to grasp game mechanics. It's based on whether a group of more conservative adults feel the subject matter and language is suitable for a child of a certain age.

Children tend to be more intelligent and capable of learning that many adults want to give them credit for. As some pointed out, attention span and patience are usually more of a problem.

With those out of way, I'm curious about the comparison between FFXIV and GW2 when it comes to learning how to play a job. I haven't played GW2 myself so please correct any misunderstand I have if you do player it.

My understanding is that while you can learn a fair number of abilities, you can only choose to have a small number active (4-5) for use at a given time. If that is true:

How much time has your daughter spent playing each game?

What does GW2 do to teach its players how to play a job that FFXIV isn't doing?

Is she making full use of the abilities available to be used in GW2 or just sticking to a couple of them like she does in FFXIV? Has she learned to add/remove abilities to change them for certain situations?

Does GW2 completely remake jobs on occasion like FFXIV does?

Does it have extensive tutorials on playing a job?

Is there anything else it does different when it comes to teaching a player their job?

With respect to adding job tutorials in FFXIV, as Mikey_R said it's pretty unlikely because that could mean completely rewriting any tutorials if they make substantial changes to a job. As it is, the original class quests that had been like tutorials are now pretty awkward because indirect references are made to how abilities act in combat but the actual abilities aren't learned until later. The level 5 Archer quest is a good example - at one point the dialogue says "For instance, you may choose to prime your weapon well and strike hard, or employ toxins to sap their strength over time.". Those are references to Heavy Shot and Venomous Bite - but the latter isn't even learned until level 6 now.

As nice as job tutorials would be, I doubt they would be practical to create until the game is truly on maintenance mode and there will be no further updates to jobs.