Is spell dmg worth at high levels?

[LudicSavant]

rather than being "canonical" single-target damage spells.

There is nothing "canonical" about you personally defining "single target damage" to exclude options like Crown of Stars, Heat Metal, Scorching Ray, Magic Missile, Chaos Bolt, Spiritual Weapon, etc etc.

That's not the way I'm using the term, nor the way that it's been used in context of much of the larger thread discussion.

Ultimately, it doesn't matter whether you call it a single target damage spell or not. It matters that it does the job.

Also, there are still good spells that don't have the option to target new creatures on future rounds, or split, or anything. Like, say, Dissonant Whispers, Mental Prison, and Mind Spike (but for all I know you may not be counting these either, since they all have an extra effect besides pure damage).

Edit:

Edit to add my opinion, rather than just responding: I think high-level damage spells can have their place, but barring really rare circumstances I pretty much wouldn't ever use them. Those slots typically just have more interesting and potent uses to me. At higher levels those "spare" low-level slots might get used for single-target pure-damage spells... but even then, I'd normally only prepare/know ones that have something beyond single-target damage to offer (like being optionally multi-target or opening up action economy options [even better without concentration], not-so-coincidentally!).

PhantomSoul, all high level mandatory single target damage spells have some additional effect beyond pure damage. Even the lousy ones.