Witchy gear (The Witcher 3: Wild Hunt)

Hello. I'm level 41 in the game right now. I did the grandmaster set of the cat school. And there was a question. Further, as the level of the character increases, you will be able to find armor with improved characteristics. I may not understand something, but why spend so much resources on this armor? Maybe it can be improved somehow. In one person's video, I saw that he had this very kit had the recommended level of 80. How so?