The Ninja 250 is never going to be a bike that has any significant amount of low end torque. You won't get it to be twitchy like a big bike.
The stock CV carbs have a natural lag built in to them, but it's not that problematic. From idle to about 3k rpm, power and torque will be low, so twisting the throttle and easing out the clutch closer to 3k to launch the bike may take away what seems like a bog or lag.
Many have made the low end power a little better by either installing a jet kit or shimming the needles.
There are also
several other performance tips that can make overall driveabiity better.