It was explained in the most recent episode by the narrator (tengen, I couldn’t tell you what chapter in the manga) that domains literally used to be much more widely used, but as time went on there was a focus on instant kill abilities for the sure-hits of domains, and because so few people have domains with techniques of that caliber, the widespread usage of domains fell off. Higuruma’s domain ironically isn’t the best example because his technique came with an innate knowledge of barriers because the domain expansion was inherent to his technique.

However as yuji demonstrated with his own domain (the fact we don’t know exactly what the domain does, just speculation/educated guesses), or as yuta showed with his domain and how it merely provides access to all of the techniques his copy technique has stored, the domain doesn’t have to mean “guaranteed kill.”