Kimchi are not preferred to be added directly to soup. Usually you would fry the Kimchi (ideally in Sesame oil) to slightly transparent or having minor brown on the edges, before adding into the soup, and boil for . That is not only applicable to KimChi JiGae- but also other varieties of KimChi broth (e.g. hotpot, Kimchi ramen/noodles (BuDae JiGae) etc.)
Adding Kimchi directly to soup/broth and boil is more a Northern Chinese way of cooking (where Kimchi is not called kimchi but literally called "Spicy Pickled Cabbage").
Frying beforehand and adding directly to soup/water can taste very, very different.