as the lower control arm does its job of traveling up and down vertically, the strut rod end at the control arm swings up and down in an arc, moving the control arm slightly front and back
Yeah but it's a TINY amount. The strut rod is longer than the LCA so the arc is larger, and the arc it travels in is at an angle to the LCA which minimizes the effect of the LCA's vertical travel.
And, if you install larger torsion bars you reduce the amount of suspension travel, reducing the distance both the LCA and strut rod travel along the arc. That's why the adjustable strut rods have to be carefully tuned for their length, and why they're superior to the non-adjustable kind. If the length of the strut rod isn't matched properly, it causes binding in the LCA as it travels. Which is true even in the stock system with the rubber bushing, the LCA doesn't like to flex very far in either direction, hence the binding. But it's more important with the poly bushings because they flex even less.
