Direct damage spells are already the suckers option. A we'll played wizard focuses on ending fights by removing the bad guys options to fight. At low level, casting levitate on a foe and having the team pelt it with arrows is a far better use of a 2nd level slot than acid arrow or scorching ray. Haste is the most damaging 3td level spell besides fireball. Wall of force prevents more damage than any abjuration and you get miles more utility out of conjuring creatures, animating objects or even animate dead. That's all before you get the fight ending spells like forcecage. And for spellcasting enemies, there is counter spell.
Couple that with instantaneous travel, the ability to move undetected, to safely scout an entire dungeon, and simulacrum shenanigans, the worst thing you can use your spell slots on xd6 damage.
And that's part of the problem.
I like how you qualified
Haste as the most damaging 3rd level spell -besides-
Fireball.
And hey,
Levitate -can- shut down a single enemy that uses exclusively melee attacks but also...
Poke the Wizard with a pointy stick. ESPECIALLY at level 3/4 when
Levitate becomes available. Also maybe try to include ranged damage capabilities for your NPCs. Even if it's just an improvised weapon like a rock you can break that concentration pretty easily.
Haste, similarly, stick-poking. And then watch whoever got Hasted suck wind for a round instead of doing anything useful. ESPECIALLY aggravating to your party members if the stick poking happens after
Haste is cast but before they get to benefit from it.
Wall of Force, though. Also Ice or Fire. And Stone. REALLY good spells to change the shape of the battlefield and force enemies to move rather than take actions in order to delay their damage dealing on the party. That's a good thing and should probably be part of the focus of the Wizard...
Of course firing off a
Cone of Cold to hit up to 78 enemies for 8d8 each... But then, why choose between the two?
Round 1:
Wall of Force to make the enemy cluster on the one side of the pass you left open for them to approach.
Round 2:
Cone of Cold to wipe out scads of the enemy where they had to cluster to try and get around your
Wall of Force.
Or, y'know,
Fireball if you wanna conserve high level spell slots and the damage falloff isn't -too- bothersome, though that's gonna depend on the specific enemy type. 24 fire or 36 cold on average still knocks out about half the HP of a typical CR 3 enemy. And if they're in large enough numbers to fire off big AoE they're far more likely to be CR 2 or 1 where 24-36 drops them to their knees or kills them outright.
Of course if it's a -single- enemy and you're throwing up a
Wall of Force you're either trying to get away or giving your party some breathing room to use healing... 'Cause otherwise you've just screwed your martials and other casters up on -their- turns trying to attack the enemy...
But in that situation?
Counterspell is also an option. For the enemy. On you. Because, again, it's a two way street.
And, of course, you could instead make it a
Wall of Fire instead of Force and make however many enemies are there take 5d8 if they're next to it, 5d8 more if they pass through it, and 5d8 more if they end their turn near it. Also only a 4th level slot and still breaks line of sight/effect. And -then- you drop
Cone of Cold. Because you don't have to choose between doing damage or controlling the field, you get to do -both-.
But, y'know. YMMV based on the situation the point is they can do both as it stands and since one is concentration they can't stack a ton of -that- specific kind of spell as active at once, but can maintain one -and- do a boatload of damage beside it.
BECAUSE THAT'S THE POINT. You don't have to pick 'Either' unless casting
Wall of Force instantly ends the encounter. You can pick BOTH.
Yes, a Wizard who fills up all their prepared spells with damaging spells is a fool. Because you can use the same damaging spells a LOT. So having 2-3 "Good" damaging spells that cover single target and AoE damage is really all you need (on top of, say, 1 or 2 damaging cantrips) and you fill the rest of your spell slots with cool effects like
Wall of Force or
Silvery Barbs or
Counterspell or
Dispel Magic. Because you can do -both-. You're not limited to one or the other and they synergize REALLY WELL if you've got any clue of what you're doing.
The question is: Do you want
Wall of Force and
Counterspell and
Dispel Magic and
Clone and stuff to be spells that exist or do you want Wizards to just be really good at dealing damage? 'Cause, really, those are your choices unless you decide to cap the game off at level 10 or something similar, which is an annoyingly common direction for people to want to go.
... also
Wall of Force should never "Instantly End the Encounter". Even if you wind up putting the dome over a single powerful enemy it should just be a delaying action, really. 'Cause within the next minute or whatever that dome is going to come down. Either because you and your party are 'ready' to fight the BBEG who has been monologuing for the last 10 rounds from inside the dome, or because one or several of his minions worked together to Geek the Mage and brought the dome down.
MAYBE it can be a "Run Away" spell, but if you're dropping a 6th level spell to drop a cup on a spider before fleeing then it's probably -really- good you had the cup.