Magic
in D&D 3.X was ridiculously OP. This is in large part because D&D 3.0 decided to take away almost all the restrictions on the wizard. But D&D 3.X is, depending how you count, between one and three editions of D&D (are 3.0 and 3.5 separate and is Pathfinder D&D?)
Magic in oD&D and AD&D had different restrictions - like the spells you knew being random. I have in front of me the 2e PHB
The reason most wizards played wizards who specialised in a school, despite all the penalties, is that they automatically gained one spell of the school they specialised in which could be selected by either the DM or the player. If they didn't they didn't get any spells that weren't treasure.
To repeat myself:
Every single spell a 2e wizard knew was either given to them by the DM. Either directly as treasure or by direct approval in a single school. If the 2e wizard was strong it was because the DM had personally given them those spells.
Also you cite Treantmonk's guide. - which is 3.5 specific. The general principles apply to 3.0 - but beyond that it's more applicable to 4e wizards than it is to 2e or earlier.
This is really good advice
for playing 3.5. It is bad advice
for playing 2e.
Battlefield control wizards and debuffers were both given exactly the same massive and unintended buff when 3.0 came out - and that was the complete revamp of the saving throw system from an effects-based gamist model to a simulationist model. In 3.X your saving throws are Fort/Ref/Will and any well-prepared wizard should be able to pick a spell to hit the target's low save (and in 3.5 spell resistance wasn't really relevant because basically the entire conjuration school ignored it).
The pre-3.0 saving throws on the other hand were far more functional. The saving throws were in order of priority and in general in order of ease of passing:
- Paralyzation, Poison, or Death Magic
- Rod, Staff, or Wand
- Petrification or Polymorph
- Breath Weapon
- Spell
(Note: Breath Weapon vs Spell was very class-dependent, and Petrifications and Polymorphs were often easier to pass than staffs, doing some interesting things for powerful magical artifacts).
So a direct fire
Fireball wasn't paralysation, poison, or death magic. It wasn't cast from an item. It didn't petrify or polymorph. And it wasn't a non-magical physical effect. Which made it use the Save vs Spell - i.e. the hardest category for the target to save and even if they managed to save they'd still take half damage - and 2e NPCs had far fewer hit points than 3.0 (which in turn have fewer than 5e)
Meanwhile Stinking Cloud in 3.0 is pretty universally considered superior to Fireball and for good reason. But in 2e it's a Poison effect. Which means that it's in the single easiest category for a target to save - and that applies to almost any target. Also if the target saved it was a waste of a spell and an action other than for the fog cloud. Even as a second level spell 2e Stinking Cloud was not that hot.
As for buff spells, these were often good (stoneskin was excellent) - but Haste was a particular stand-out. It aged the recipients by a year, and being magically aged by a year meant a System Shock roll; Haste was quite literally a save or die spell on the target you cast it on. So for that matter was Polymorph which also triggered system shock. And just trying to cast Wish. Teleport gave a chance of the wizard teleporting above or under the target. Under, of course, being an instant death if they teleported into something solid.
So please stop talking about "prior editions" when you mean 3.0 and 3.5. 3.0 basically removed almost all the balancing factors for the wizard such as not getting control over the spells you knew and not getting to pick the saving throws and accidentally killing your allies or even yourself through spellcasting when you were using the spells as intended (and not e.g. a ground zero fireball or a reflected lightning bolt - and those went too).
5e brought precisely none of these balancing factors back (or the level soft-cap). It did however bring other less-stringent balancing factors back and has as a result what I believe to be the third strongest wizards of any D&D edition (after 3.5 and 3.0).