If the barrier is just "raw magic power", would it be smarter to absorb the magic of the barrier to attack hard enough to wipe out all enemies?
Or absorb the magic of the barrier to create a bigger barrier outside? Make it smaller until it smashes everything inside?
That girl was able to manipulate that dragon vein thing, which people can barely understand or feel, so manipulating that raw magical power would be a piece of cake, right?
In addition to all this, there would be 2 people to control the barrier, to charge a big attack or crush them inside a better barrier.
Jump inside the barrier, risking yourself in a dangerous position, which would take a long time to recover magic after the battle, and in addition, have a limited self-imposed time to finish a fight that you admitted to be difficult before even starting. .... This seems very complicated, inefficient and stupid, not to mention that your witness will only be able to see your allies fighting the monsters, because you are inside the barrier and he will see nothing.
I am disappointed.