Final answer:
The claim that instrumental improvisation overshadowed vocal performances during the Swing Era is not true. Vocalists like Bessie Smith played a significant role alongside instrumentalists in popularizing jazz music.
Step-by-step explanation:
All of the following are true of singers during the Swing Era EXCEPT: d) Instrumental improvisation overshadowed vocal performances. During the Swing Era, vocalists indeed played a crucial role in the popularity of big bands. Singers often fronted these orchestras, and scat singing became an iconic vocal technique. However, the assertion that instrumental improvisation overshadowed vocal performances is not accurate. In reality, vocalists such as Bessie Smith and her collaborations with artists like Louis Armstrong highlighted the importance and popularity of vocal talents alongside instrumental elements in jazz music. Furthermore, the influence of Black musicians from the Harlem Renaissance to the genesis of jazz and its spread to wider audiences shows that vocal and instrumental performances often enhanced each other rather than one overshadowing the other.