Goal: To give each Archmage specialty its own unique usefulness. To make Archmage live up to its title, not Mediocre-mage.
Abjuration School changes: This is the worst school by a wide margin
Shield SLA, can be cast on self and others (to indicate the Abjuration specialist's mastery of their chosen school)
Change Protection from Elements to Glyph of Warding (I realize this is a divine spell but it seems so much better than the same level Fire Trap)
Change Dismissal to Banishment (Banishment has limited usefulness, especially with the inflated HD issues of DDO, but its the best Abjuration gets)
Conjuration School changes:
Change Cloudkill to Everard's Black Tentacles
This has always been a wiz/sorc spell but I understand the devs wanting to keep some uniqueness to the warlock spell list.
So this is a compromise that only Conjuration specialized Archmage would have access. Cloudkill is a terrible spell in DDO because its determined by the target's HD and as we all know enemy HD go off the charts eventually. Speaking of which epic ward prevents or severely curtails ability score damage also neutering Cloudkill's usefulness. Finally, web looses much of its viability as CC when enemies as well as teammates spew fire on the battlefield so Tentacles would give this school a late game CC.
Enchantment School changes:
Change Resistable Dance to either Charm Person or Touch of Idiocy
(I know most people don't use ToI but I like to use it in the early game to prep a target for Charm or Hold and a cheaper version of this could be useful to an enchantment specced Archmage even at higher levels.)
Change Hold Monster to Mind Fog
(Same reason really, in later gameplay I rarely if ever used the single target SLA versions of Hold/Charm but Mind Fog was useful to blanket an area and reduce enemy saves.)
Evocation:
Evocation is what it is, the only possible change I might make to it would be Fire Shield to Force Missiles but some people really like their constant up Fireshield so...? Up to popular opinion I guess.
Illusion School changes:
Alright Illusion has the least number of spells but is in a decent place right now however these are the changes I would make...
Displacement self only version same as now AND a 2nd friendly version that can't be extended (to indicate the Illusion specialist's mastery of their chosen school)
Change Shadow Walk to NEW Weird (Should work very similar to Phantasmal Killer but instead of single target it should affect multiple targets, still has all the saves, SR and limitations of PK and likely a longer cooldown.)
Necromancy School changes:
Possibly change Halt Undead to Ray of Exhaustion. (Reason is Halt Undead has limited usefulness when it only works on undead and no more than 3 at a time. Basically would rather use a web in most cases for the same purpose.)
Possibly change Waves of Fatigue to either Negative Energy Burst or Death Aura. (Reason is - I think either would be more useful to a late game Necromancy specced wizard than Waves of Fatigue which will soon be replaced entirely with Waves of Exhaustion when that type of effect is needed.)
Transmutation School changes:
This one is very difficult. Most of its best spells or rather just most of its spells are 6th level spells. Perhaps the ability to cast Tensor's on party members unextended (to indicate the Transmutation specialist's mastery of their chosen school) would give this more niche.