Complex sentence: The parallelogram rear derailleur had gained prominence after Campagnolo's introduction of the "Gran Sport" in 1949, and the slant-parallelogram was an improvement of it that allowed the derailleur to maintain a more constant distance from the sprockets, resulting in easier shifting.
Split into simpler sentences: The parallelogram rear derailleur had gained prominence by Campagnolo's introduction of the "Gran Sport" in 1949, and the slant-parallelogram was an improvement. It allowed the derailleur to maintain a more constant distance from the sprockets, resulting in easier shifting.