I do see your point. What are good alternatives then? What do you think are the least bad scaling wizard spells in slots 5-8?
Animate Dead seems to scale well. Hold person is situational. Banishment should be decent too. Are there any more?
The best scaling spells could be its own guide!
Great question though. Keep in mind this could use more research, but with a quick look, some options I notice are:
Blindness/Deafness is a great spell for scaling (one extra target per level, 2nd level spell), and IMO is a much better option than hold person as it doesn't use your concentration and is not limited to humanoids.
Someone mentioned Animate Dead - also note that if you are a Necromancer, this becomes even more pronounced. Also doesn't require concentration.
Eventually you will get 5th level spells, and then Animate Objects is going to be your go-to spell for higher level slots - and it does scale decently. A much more effective way to do damage.
There are likely many more examples (Using Bestow curse (3rd level) with a 5th level slot comes to mind)
You should take into account that "gish" builds are not my specialty, so take my advice with the appropriate grain of salt.
I'm actually a fan of the Arcane Trickster/Wizard split. Use cantrips and lower level spells (like scorching ray) for blasts (+ sneak attack damage) and higher level slots for debilitating spells.