Question

How is using the word wither more impactful than using other works like weak​

Answer 1

First of all, wither is better compared to weaken, rather than weak. But to answer your question, weak is a very general word that can describe many different circumstances. Using wither is more impactful because it gives a sense of what specifically is happening without even expanding on it. The more specific and precise you are with verbs, in most cases the more impactful they are.