That is entirely different from the view that all instrumental music is forbidden.

Let alone that all music, instrumental or vocal is forbidden.

Nobody would say the Russians are slackers in the instrumental music department*. Yet both Rachmaninov and Tchaikovsky wrote a capella music for the Orthodox Church as well. (Indeed I have sung some of their music in church -- Tchaikovsky's "Holy God" ("Svyati Bozhe") is gorgeous.)

*prompting the Rolling Stones to write their famous song, "I know you own a rock-and-roll balalaika".