It's a bit of a misnomer that fast twists don't shoot roundballs well. Original jagers from the 18th century have twists down to 1:28" and 1:30" and were designed and used for balls.
What's more important is the depth of rifling. Originals had very deep rifling and therefore allowed the prb or bore sized bare ball to engage the rifling well even with fast twist. Nearly all modern factory offerings have shallow rifling which makes the twist rate more of a determinant on projectile suitability.
Even fast twist shallow rifled barrels can shoot balls reasonably well provided you use a lower charge.
What's more important is the depth of rifling. Originals had very deep rifling and therefore allowed the prb or bore sized bare ball to engage the rifling well even with fast twist. Nearly all modern factory offerings have shallow rifling which makes the twist rate more of a determinant on projectile suitability.
Even fast twist shallow rifled barrels can shoot balls reasonably well provided you use a lower charge.