I suppose some people might feel that a sniper having a spotter is a bit clunky too. Doesn't mean it's not a thing. A person can only do so many things in the space of a second or two.
And if a D&D spellcaster was like a sniper, that would be reasonable. But they aren't.
The D&D spellcaster has always been more like a gunslinger (to continue with your theme) - self-contained and ready to go off at the drop of a hat.

Requiring teamwork to identify and then counter a spell wouldn't be a problem if it had been part of the game from the beginning. Trying to tack on something like this in a supplement, years after the game has been released just seems like adding extra complication for no real benefit. (Unless you count annoying the player of the spellcaster as a benefit...)