Is spell dmg worth at high levels?

[LudicSavant]

4 Counterspells per round you mean?

Yes, because that's the threshold I care about -- how much it takes us to get out a Wall of Fire.

The ideal number for that is "1 slot" using the familiar method I described. The maximum (e.g. least efficient strategy + unlucky rolls) for that is 5 slots.

The Manglers have advantage on round 1 against anyone who hasn't taken a turn yet, to offset the disadvantage from Darkness, and enough HP to make it through the Wall of Fire. If the guy concentrating on Darkness happens to roll low on initiative, that Darkness might pop--yet another threat vector to worry about while the Counterspell war is raging.

These giftlocks have over 100 hp, 19 base AC, Advantage on concentration, a high initiative bonus, and more healing resources than they know what to do with. The Mangler flurry does 10.4 DPR with Disadvantage, 24.3 if it cancels due to losing initiative. I'm not worried.

BTW I don't think Synaptic Static's d6 penalty stacks with itself.

Correct, it does not stack. Why do you bring it up?