Why was samurai armor so effective and why could it be superior to Western armor?

Samurai armor was so effective because it functioned perfectly with Samurai fighting style. I am referring to the samurai armor worn during the Sengoku Period. It provided sufficient armor while also great flexibility. In comparison to western armor which I assume you mean knight armor or medieval style armor evolved from clunky to just plate armor for firearms. The difference between how the armors evolved was the time in which firearms were introduced to Japan.

Explanation:

As the Age of the Samurai came to an end in Japan and they pushed to form a modern army. "armor" in the militaries of the world was just clothes like military uniforms.