My point was that wizards who weren't outright demigods, monsters, or epic archmages would have types of magic they couldn't do.
This forced them to either rely on nonmagical skills and knowledge or defer to allies to overcome so obstacles. Nor because they didn't prepare them but because they could not do that type of magic.
Often the adventure was to find the one thing or person who could perform that type of magic. What D&D did was magic the unique into the mundane as wizards who learn anything. There was no notorious necromancer who could raise the dead or famous wizard who could speed up time. Either of these wizards could learn the others spell.
Again, so? I don't see the relevance of this to the point I was making. It is a nonsequitor to the idea to which you responded.
Let's say a necromancer and a chronurgist were engaged in battle. Each has their focus. Let's say that each is also only limited to their focus. Which of the following is more evocative and interesting?
Necromancer: I use Vampiric Touch ... 19 to hit ... and ... deal 22 damage. I heal 11.
Chronurgist: I cast Slow on him. DC 16 Wisdom.
Necromancer: 18 save. I cast Danse Macabre and have the 5 skeletons attack. 13,16,8,15,18.
Chronurgist: 2 hit.
Necromancer: 7 and 6 damage. Total 13.
Chronurgist: OK. Time Ravage? DC 16 Constitution. 85 necrotic damage if you fail plus a buncg of effects. Half on a successful save.
Necromancer: I'm resistant . Fail the save, still take 42.
Chronurgist. But you die in 30 days, have disadvantage on attack rolls, saves and ability checks - and move half speed. You need a 9th level spell to fix it.
Or:
Necromancer: I use Vampiric Touch ... 19 to hit ... and ... deal 22 damage. I heal 11.
Chronurgist: Wait a second: I cast slow as a reaction. When cast this way, it gives you disadvantage on the attack. As you rech out to hit me, I use the slow magic to give me a chance to dodge!
Necromancer: Doh! 12 ... that missed, right?
Chronurgist: Yup. OK. I'll go for Time Ravage. DC 16 Constitution. 85 necrotic damage if you fail plus a bunch of effects. Half on a successful save.
Necromancer: I use Tether Essence's reaction - make a Constitution Save yourself. DC 17.
Chronurgist: As a reaction I use Temporal Leap and jump forward 1d6 rounds in time, avoiding the Tether Essence.
Necromancer: Nice. I'm resistant. I fail the save, but still take 42.
Chronurgist. But you die in 30 days, have disadvantage on attack rolls, saves and ability checks - and move half speed. You need a 9th level spell to fix it.
Necromancer: OK, but I'm casting Danse Macabre to get ready for when you reappear.
This is not a new idea, but it is an idea that has never been executed well in D&D. Instead, we drop a few reaction defense spells in the game and call it a day. They get kind of boring. I'd rather they dropped shield, absorb elements, silvery barbs, counterspell, and other reaction defense spells in favor of giving each existing spell a reaction use that was defensive or battlefield control related (grease, web, etc...)