I think Kishi knew Sasuke wouldn't affected by losing an arm. Look at The Last, Naruto Gaiden, and Boruto Movie Lord Sasuke more savage with one arm than he was with two. Only God knows what will happen if he lose his other arm. He might start to solo reality itself. Kishi probably thought Naruto wouldn't be good with one arm. Can he even do Rasengan with his left? It took him 3 years to learn the Rasengan with his dominate hand.