Dia IV is a bad example considering it's really not that hard to cap attack. Saying that an enfeeble can't work is just not looking at a wide enough scope. For example if we got an enfeeble that caused the monster to take double damage from everything well...Red Mage would likely be the most wanted job. Now obviously that example would be over the top a bit, but enfeebling doesn't necessarily have to mean a defensive effect and it doesn't JUST have to mean defense down. There are weaknesses to enfeebles as well though, mainly that trash monsters die too fast. If a monster dies in 3 seconds that's hardly MP efficient to try and keep an enfeeble on every monster though at the same time you can debate if the increased killing speed at that point is really worth it.

Likewise, Enspells only affect the TP phase which Red Mage has generally NEVER had problems with. Red Mage throughout the history of FFXI has generally been one of the best DoT jobs. It's always been the Weapons Skills that blow us out of the water and it's been those Weapon Skills that always created the huge gap between Red Mage and other DDs (that and leg selection D. Now with abyssea things have become slightly inverted now. Our Weapon Skills are actually decent but now our TP damage isn't so hot due to our enspells not scaling as well and the fact that we generally are forced to use a lvl 75 dagger in the main hand.

I'm all for T3 Enspells what their effect will be will depend a lot on where the content of FFXI is going imo. If we are going to keep atma then sure, create some broken enspells, but if they ever want to leave abyssea at some point either they will have to balance them so that they are insignificant inside abyssea or that they will have to scale with atma in someway (besides elemental affinity).