Tell you what, a single Templar won't overpower my influence over reality, nor will a bunch. if I face like 50, who will all focus on blocking me out from the fade, I'll switch to the taint instead.
Also seekers draw their powers from the fade as well, so don't clump them together with Templar abilities.
Three things.
A few dozen Templars overpowered the largest concentration of magical energies in the modern age along with the anchor.
So thinking that fifty would be required for a single mage is amusing grand standing or being OP either way it's more a joke to me.
Two the Taint can be magically negated as well.
It's spell casting is not protected or immune.
Three Solas inferred it was the same in principle for both orders.