It sounds odd, but the biggest result of the prop turning is actually a yaw to the left. There really isn't a rolling reaction that is at all noticeable. So, you counter the engine effects with either rudder or right thrust.

Note the above where the Nextstar with no right thrust has a tendancy to turn left at times. That's what you'd expect. The same effect causes planes to tend to pull to the left when you go to take off, requiring you to use the rudder on the takeoff roll. The amount of right thrust you "need" to keep the plane tracking straight varies with the airspeed and engine speed (and prop and other factors), so the right thrust built in to the plane is the compromise the builder decided to go with.

The Nextstar was probibly designed for lots of slow flight (which, given that it's a trainer, and comes with airbrakes, isn't much of a surprise). If you spend a lot of time at low airsped and higher power settings, you find you want more right thrust. If you fly faster, the vertical stab and rudder have more effect, and you need less right thrust.