SUGGESTION: Turn Bluemage into a regular job - Limited Job>Advanced Job (An Approach)

[MaraD_]

if AM simply just became a stance that gave BLU all 3 abilities, instead of one role one, to replace missing traits other casters, healers otherwise get for those level gaps.

I can mostly agree with what you're saying, but I feel the need to elaborate on how I imagine it could have been done. (I know, everyone, including me, thinks they have the solution...)
(The following is based on a blank slate design)
IMO, the spells should come with... (for lack of a better word) "role stats". Not the usual stats, but ones that are only seen in the ability select menu, and they ONLY effect blue mage spell cast time/effectiveness, and not primary stats. They pump eachother up, based on being of "the same type", or Hinder ones of "opposing types".

Also, have a BUNCH of neutral weaker spells, which dont fall into a category, so they cant hinder, or buff the spells you pick. (essentially filler moves, or ones that are decent for tanking/healing, since this is where most of their DPS come from, w/o hindering thier tanking/healing)
(IMO Cast time is the most effective way to do this. Make the cast times to exceed the GCD by default, except neutral spells, so that you KNOW its a DPS loss to use the wrong spell type, but if the emergency is big enough, it may be worth it. Only by stacking spells that lower the GCD, can you reach the basic GCD cast times, or even lower, to help weave in oGCDs)

Obviously theres so many spells already made, that this system would be a lot of work, to rebalance everything, but its a starting point imo.
The idea is mostly based on how BLM, SMN, and RDM are balanced to eachother. (BRD thrown in for example)
Selfish DPS spells stacked together increase DPS (BLM build). Supportive DPS buffs decrease self DPS (BRD build). Minor Healing option lightly hurts DPS (ex:SMN with rez). Large healing utility hurts DPS a lot (RDM build).
Going from DPS to tank, in case both tanks go down, or going full healer, in case healers go down, is good enough, even with penalties. But you need to decide before the fight, if you want to be a pseudo tank, who can only hold the boss for 30seconds if the tank goes down, or if you want to put all of your abilities into tanking abilities, to try and off tank/tank swap as a full time replacement tank, because tanks arent showing up in party finder, or your raid groups tank had to drop out for the night. This would be more than acceptable, because both possibilities are there.
I do understand why you said they should have more abilities attached to the tank stance, but i disagree, if your threat is relatively close to the other DPS, and you pop tank stance, you should be main threat in like 1-2 GCDs (if they made the stance reasonable), and be able to take auto attacks fine. Tank busters are where you're going to have an issue, but a "temp tank" isnt meant to fully main tank for long periods, just for short bursts, until the situation is under control. (which in most cases, a tank buster shouldnt be coming out after a tank just died, as the tank probably died to a tank buster in the 1st place.)

EDIT: I also feel there should be 3 DPS styles, but thats going too far in having SE trying to balance one job. (Melee, Cast Range, instant cast range, each with their DPS penalties, depending on ease of use)