Is spell dmg worth at high levels?

[PhantomSoul]

Would you also object that Fighters do not deal single target DPR because they can choose to attack different targets on different rounds?

You can re-label it whatever you want -- the fact of the matter is that these spells are effective at eliminating big individual targets via damage. They fill the role.

Likewise, things like Magic Missile and Scorching Ray and Blade of Disaster and Bigby's Hand and so forth are capable of hitting multiple creatures within the duration of a single spell, but clearly excel at the single target damage role.

I wouldn't call the Fighters a Spell, which is an important difference! (I recognise you're not saying they are -- but there's a difference in comparison.)

The Spells are more like the Berserker Barbarian's Frenzy giving them a[n extra] Bonus Action option to Attack or like Haste [at least in my experience, it's usually being cast for the extra Action, not for the +2 AC or other bonuses], to me. And it not being restricted to a single target for the whole casting is a meaningful difference to me, but here it's more like adding that Fighter (boosting Action Economy) than like giving an existing Ally bonus Damage.

(I also think Magic Missile giving you a choice of targets is an important benefit, and it has come up regularly at my tables. If anything, it's probably been used as a guaranteed way to finish off one or several targets while hitting multiple targets much more often that not!)