> So my mental model of commands in vi is that "nC" is the same as executing "C" n times. Your mental model would be correct for motions (2j, 3w, 4}, 5][, etc.

> So my mental model of commands in vi is that "nC" is the same as executing "C" n times. Your mental model would be correct for motions (2j, 3w, 4}, 5][, etc.) but J is not a motion. From :help J: > Join [count] lines, with a minimum of two lines.