One of the major issues I have with debuffs and why I don't think the way they work with the current game would support a debuff class such as Red Mage being added in the future is that SE currently pick and choose when your debuffs work in all fights of consequence such as primals and raids.
Most of the time if a debuff lands on a boss it's usually part of the fights mechanics. Such as Ifrit and stunning Eruption or ADS and silencing High Voltage. The rest of the time these effects are simply turned off, reducing your abilities to their base form of pure DPS.
I can understand it is probably easier to balance a fight by turning off these debuffs but I can't help but feel it cheapens these abilities if they only work when the developers decide they will, and takes away from what could be a much richer in flavor and dynamic combat system in boss fights.
I know it's probably a personal gripe but it always is disheartening, for me at least, to enter a boss fight and see my abilities lose half of their effectiveness simply because the fight hasn't been balanced to make use of them.