I'm one of the people that is dissatisfied with Inquisition's mage abilities, but it wasn't so much the abilities themselves as it was the scope. Sure, Energy Barrage or Ice Mine can serve the same essential function as a Hex from Origins or DA2, but I really like the thematic element of having an actual dedicated hex or glyph of paralysis. Making everything elemental made everything more...one-note, imo, even though what was there worked really well.
The Glyph of Paralysis still exists. It's just in the form of an ice mine. It comes with perks too 
Of course like I said before, if you simply like to cast spells every other second, then clearly you'll enjoy the DAO style more.
I never thought that Inquisition's spells were bad, just that they are all thematically way too similar.
I don't think I can agree with this. Each tree has spells that function differently with different forms of CC and disables attached to them.
No two spells are alike.
Compare a single target ability in Winter to one in Inferno.
Winter's Grasp: 4-sec duration low-damage single target CC that upgrades to a small AOE
Flashfire: 8-sec duration medium-damage single target CC that upgrades to a longer duration
The former freezes a target(s) for a short duration and an be combo'd with a crit for a giant nuke
The latter interacts with abilities that are enhanced by the Fear Debuff. It also acts as hard CC.
What about the AOE damage spells?
Winter has one, Blizzard, which is toggleable and affects enemies with a slow debuff.
Inferno has three. Immolate acts a small AOE nuke with a DOT, another as a wall of damage, and the third as a HUGE trigger mine.
The passives are entirely different, with Winter spells focused on mana regeneration and defense while Fire passives focusing on dealing huge damage passively or with barrier.
How do they feel the same? I can do this again with Storm
pretty much every mage will end up specializing in Elemental magic because of lack of options. You can do a Spirit mage + Specialization, but that's pretty much it.
This is an odd argument.
First of all, you're chunking all the trees into the Elemental Tree. How is this different than specializing in Primal, Elemental, or Spirit, the three damage-oriented trees in DA2?
How is it even functionally different than Dragon Age Origins? You have four trees, each with 16 abilities that are often redundant, mutually exclusive, or upgrades of one another.
Every game had four main trees to choose from. There are less spells in Inquisition, but that's largely because redundancy was removed and sustains incorporated into abilities or passives.
The support tree in Origins consisted of the three tiers in Creation as well as two tiers in Spirit. In Dragon Age Inquisition, this is mostly relegated to the Spirit tree, but the specializations themselves have been vastly improved to potentially incorporate support spells.
While I miss Creation and the ability to heal, I can't say that Spirit Healer ever felt powerful in Dragon Age.
Group Heal was the only useful ability in the DAO specialzation, as the remaining spells were functionally weak or pointless in the vanila base game. Combat Tweaks made them better, but that's modded.
In Dragon Age 2, using Spirit Healer blocked you from casting any offensive spells and drained your mana. The base abilities were weaker than in DAO, only surpassing it when upgraded.
At least the Spirit tree encourages gameplay with other trees. Inferno mages gain damage from it. Knight-Enchanter mages charge it... etc...
All three specializations in DAI can function as support trees if you play them as such much like in DA2. Your Knight-Enchanter can be a tank WHILE being useful with their spells unlike the Arcane Warrior. The Necromancer can CC like a boss.
....
I also don't see the argument on how mages feel "all the same".
At early levels, you can specialize in one tree or mix and match across four trees. When you access your specialization, you can only pick one for the entire game and it completely changes how you play. Knight-Enchanter makes you melee, Necromancer encourages brinksmanship and CC, and Rift Mage encourages AOE gameplay.
Now if you make each companion play with different spells and use them all, then naturally you'll exhaust most options but it's always been this way.
Morrigan goes Primal and Entropy. Wynne goes Creation and Spirit. Er... my character goes Primal and Creation... oh I've seen this before... 
Your character though can have dozens of potential builds to play for the major part of the game.
When you get to higher levels, then the natural power creep of RPGs kicks in and you start investing points in skills you don't need for passives that you want or whatever. I think it's safe to say this happens in all games. In DAO, I would start taking spells I don't even remember to get to ones I care about.... like Crushing Prison making me take Telekinetic weapons and something else I forgot. In both DAO and DA2 I'd start having too many abilities to actually care to use around level 16+. It's even worse in DAO when I get to awakening. At that point leveling up is like a chore.
it was just super jarring for me that suddenly the vast majority of magical tools we know mages to have (through 2 games, comics, and several novels) effectively vanished.
The only arguably missing tool is direct healing and even that is not completely true. It's still technically available as part as Knight-Enchanter's focus ability, which is ironically stronger than any healing spell in previous games if fully upgraded.
Disables still exist.
Damage still exists.
Debuffs and Buffs still exist.
You can't generalize.