Well, I'll add a few to the list. As a note, I tend to give a pass to utility/World Building spells that are less of trap option, so things like Illusory Script don't make the cut (though I would change the duration on that spell to 'until dispelled' or some such).
Cantrips: The clear winner hear is True Strike. Absolutely terrible spell. I would change it to just be like Resistance, but for attacks (add 1d4 to an attack roll before spell expires, change duration to 10 min/1 hr with conc.) Honorable mentions are: Friends and Blade Ward.
1st level: Witch Bolt is another clear winner. Between the low damage, action economy drain, short range and concentration requirement; just no. I've seen many "fixes" for this spell, I'm kind of partial to having it grapple the target (with the rules for escaping a grapple applied), but that might be too much. Maybe just a range increase with a knock back or speed reduction effect. Honorable mentions: Ray of Sickness, Jump.
2nd level: Find Traps seems particularly bad the way it is designed. Honorable mentions: Cordon of Arrows, Crown of Madness, Ray of Enfeeblement and Melf's Acid Arrow. Some would add Barkskin and Flame Blade to the list, but I think they have their uses, as indeed CoM & RoE do, but they are not well designed.
3rd level: Not a lot of real stinkers, but Feign Death, Flame Arrows, Bestow Curse, and Vampiric Touch all are a bit lacking in one way or another, or are overshadowed in some way by lower level effects.
4th level: Blight, Grasping Vine & Phantasmal Killer are all candidates. All have niche uses and can be applied successfully, but seem worse than other spells at this level or overshadowed by lower level effects; or are just too little for this level a spell.
5th level: Immolation & Negative Energy Flood stand out here. Dispel Evil & Good is a bit too niche as well, with the lower level Banishment & Protection from G&E around.
6th level: The Investiture Spells are probably not really worth it at this level and Flesh To Stone is a little too restrictive for PCs to use to greatest effect(though NPC can still make use). Create Homunculus & Drawmij's Instant Summons seem to be a little over leveled, though they are more downtime/ritual spells.
7th level: Mordenkainen's Sword takes the cake here (one wonders if you could take the recent Blade of Disaster, tone down the damage a bit, and have a decent implementation of MS). Divine Word, Regenerate, PWP, and Prismatic Spray all are either too niche or lack oomph for the level.
8th level: Ali-Dalzim's Horrid Wilting seem to be the one here. Although arguments could be made for Glibness, Demiplane, & Power Word Stun.
9th level: Weird is probably the winner here. Though Blade of Disaster, Astral Projection, and Timestop could all be be contenders.