Big muscles need angles
The back grows best with a vertical pull, a horizontal row, and often a shrug or pullover, because different exercises bias different regions. One movement leaves parts undertrained.
It is about weekly sets, not exercise count; large muscles want 2 to 4 exercises, small ones 1 to 2, totalling 10 to 20 sets.
The right question is weekly hard sets, not number of exercises. Large muscles like back, quads, and chest generally want 2 to 4 different exercises to cover all their angles and 10 to 20 sets total. Small muscles like biceps and side delts often need just 1 or 2 exercises. If a muscle only gets one movement all week, it is probably undertrained.
The back grows best with a vertical pull, a horizontal row, and often a shrug or pullover, because different exercises bias different regions. One movement leaves parts undertrained.
Side delts, biceps, and calves respond fine to 1 or 2 exercises as long as the weekly set count lands in range. Piling on five bicep variations is redundant.
Two exercises at 4 sets each equals 8 weekly sets. Judge coverage by whether each muscle hits 10 to 20 hard sets, not by how many exercise names are on the list.
It is about weekly sets, not exercise count; large muscles want 2 to 4 exercises, small ones 1 to 2, totalling 10 to 20 sets.