Fanaelialae
Legend
What I mean by load up is that, in order to counterspell a wizard with counterspell, you need two mages with counterspell on the opposing team. Because otherwise the wizard can counterspell their counterspell and it's a wash. So you need a second mage to counter my counterspell.What do you mean "load up"? First, players all know that counterspell is just about the most important spell in the game. I believe NPCs should be aware of the same thing. Second, even a single counterspell can cause a Wizard to (effectively) lose a turn, which in 5e is a very big deal. You don't have to "shut down" the Wizard for it to be a big problem.
And if you replace both martials with casters? Sure, you may get lucky with saving throws and lock them all up, but if something goes wrong, and one monster gets loose and causes a caster to lose concentration, freeing another monster from control, things can get out of hand pretty quickly.
The game works best with a mix, in my opinion. Working as intended.
They also need to remain within 60' of the caster they're shutting down for it to work, which generally means sticking quite close to the wizard, since basic movement will get you about half that (and I only need to be 65' away from them on my turn for this to be effective - it doesn't matter if they get within 35' on their turn).
So clearly if you say that you are counterspelling me on round two and every subsequent round as you claimed, you have two mages that are sticking within 30' of my wizard at all times. You say you've run high level campaigns and you use counterspell like this to challenge your players, yet you're not aware of these prerequisites?
You have to play differently without martials, it's true. But casters like clerics, druids, and even bladesingers can be highly effective at filling in for those roles, while still doing their own roles effectively. I've run sessions where the martials couldn't make it, and it isn't as big an issue as you seem to believe.