There are 2 reasons why GL Bardiche has worse stab than the NCS. Realism, and Balance.
Balance:
GL Bardich has waaay more reach and waaay more cut damage. It can rear horses, and break shields.
NCS is faster, can be used with a shield, and has a slightly better stab.
If the GL Bardiche has a great stab, or the NCS had a worse stab, they would be OP/UP respectively.
Realism:
The GL Bardiche has a curved blade...not very good for stabbing. It's like trying to shove a sharpened tennis racket into somebody. It's not going to work very well.
The NCS, while it does have a somewhat "spatulate" tip, it does have a point and a straight blade. Even though the GL Bardische can be used with two hands, you would not be able to shove that blade into something as deeply as the NCS.
What can penetrate a human body more? A sharpened tennis racket thrust with 2 hands, or a sharpened butter knife thrust with one? The knife will penetrate further. The other is just too broad for real penetration.
Now put the tennis racket on a long pole. It becomes imbalanced and harder to control exactly where you're stabbing. This makes it even harder to penetrate into a vital spot.