Then you may as well say it should be a normal job. Like I have said countless times in previous posts, Limited Job is a system and if we move Blue Mage over to the Normal Job nothing will be lost. Limited Job is a system that is like the Normal Job system but with restrictions, to let it queue in DF you may as well make it a normal job and balance it.
Yes, there are preconceptions of Blue Mage but the key thing about what makes a Blue Mage is that they learn spells from monsters and have a wide variety of it. There is nothing whatsoever of it being an overpowered job, there is however saying the job is versatile in any given situation. So if they omitted or nerf some of the spells (Like throughout 5-11 FFs they did it and rarely anyone complains about that), let it have the ability to change its role at a certain level (Preferably at 60/70), make it a normal job. Then we got ourselves a Normal Job Blue Mage, cause at the end of the day Limited Job provides nothing and gives nothing. Blue Mage provides something and give us filler content (Which dies in 1/2 weeks).
It is like Fisher and Ocean Fishing, got all the achievement and fishes in ocean fishing? Then wait for the new patch for it to update (Which is happening in 5.4) except it is like 1 per expansion. Blue Mage has gotten two updates this expansion, which I understand in SB they only had enough patch for one update, but the fact of the matter is that they did two updates for this expansion which means something big might be coming for Blue Mage, and it may be in 6.0. I'll say it before and I'll say it again it can work as a normal job, the simplified answer is that they need to focus on giving it a job gauge and from there balancing Blue Mage will be a lot easier (Possibly). If in 5.4 they are saying they are planning something big, then I can assume they are planning on making it a normal job in 6.0 while 5.4 is the make it or break it point for them to experiment with Blue Mage right now. Level 70/Stormblood expansion is when Job Gauges was first introduced into FFXIV, so finger crossed they bring in a Job Gauge for them cause then it can finally become a normal job in 6.0.