...Perhaps you’re reading a different question to the rest of us? I understand ‘straight and level’ to mean heading and altitude control.
Ordinarily, I would agree that a question relating to straight and level flight would include both altitude and directional control, in which case discussion including the Turn Coordinator and/or Directional Gyro would be applicable.
However, the OP was asking about pitch control as it relates to altitude - hence the expanded comments about the VSI and altimeter - during straight and level flight. Thus, one can assume that the directional component of "straight and level flight" is not a concern and can be ignored for simplicity.