Many, perhaps most, branches of jazz do use seventh chords and other extended chords as fundamental parts of the harmony. The central harmonic concept in this kind of music is the tritone and tritone substitution.
The dominant seventh chord contains a tritone between the third and the seventh, which means another dominant seventh chord that has a root a tritone away from the original root shares two of the same notes as the original chord. This is a popular and important harmonic mechanism in a lot of jazz, so I believe the word "fundamental" is appropriate. In these types of jazz, I think it would be fair to say that "mere" triads are relatively uncommon. Note that tritone substitution is not ubiquitous in all jazz, and can be used in other genres.
Beyond that, seventh chords of all kinds are quite important in almost every kind of music you might hear today. Music before the baroque period seems to have occasionally used the dominant seventh chord, and by the baroque period the dominant seventh chord was important. The history of the major and minor seventh chords doesn't come up as easily in a quick web search, but they are definitely used widely, starting in the classical period at the latest, and all types of sevenths are regularly used in pop and rock music, along with many other genres.
Side note, while seventh chords are not as fundamental in genres other than jazz in the same way, you might be underestimating the role of non-triad chords in pop and rock.