Well, actually downthrust counters the effect of too much pitch stability brought on by the CG being too far in front of the neutral point. It's got nothing to do with P factor effects.

In tail draggers a strong P factor results in a bad yaw at takeoff. But there's also going to be an associated torque effect at the same time. You're certainly right though that some side thrust will deal with the P factor effect.

But many of our models will also roll into a yaw as well since many of them use some dihedral. With such models adding a bit of yaw with some right thrust will produce enough roll couple to cancel out much of the torque induced roll. So due to the design of the craft the right thrust CAN do both.