Let's humor the idea of turning Blue Mage into a regular job... Because why not..
Let's look at the list of Blue Mage spells to see which ones would absolutely have to be taken out of the class to even start, due to certain status effects included in them or certain mechanics involved.

Here's a complete list

High Voltage
Final Sting
Glower
Bristle
White Wind
Level 5 Petrify
Ice Spikes
Self-Destruct
Transfusion
Faze
Snort
4-Tonze Weight
The Look
Bad Breath
Diamondback
Sticky Tongue
The Ram's Voice
The Dragon's Voice
Missile
1000 Needles
Moon Flute
Tail Screw
Mind Blast
Doom
Peculiar Light
Feather Rain
Protean Wave
Northerlies
Abyssal Transfixion
Eerie Soundwave
Avail
Frog Legs
Whistle
Black Knight's Tour
White Knight's Tour
Level 5 Death
Launcher
Perpetual Ray
Devour
Reflux
Condensed Libra
Aetherical Mimicry
Tingle
Cold Fog
Angel's Snack
Chelonian Gate
Ultravibration
Basic Instinct
Dragon Force
Hydro Pull
Malediction of Water
Matra Magic
Peripheral Synthesis

And then most of the Trial boss attacks would also probably have to be nerfed as well with longer cooldowns and lower potency...