Basically, yes. You would use a Linear VCA for signal attenuation. The Mixer Channel unit is for adding (i.e mixing) another signal into the signal chain at the point that you insert it. Like this:
So you if you want to put something in the path of the signal that attenuates then you should use either a Linear VCA unit or the Limiter unit.
An alternative arrangement is to assign the IN1 input to the Mixer Channel’s sub-chain source. In this case (only) will the Mixer Channel gain affect the level of IN1 being mixed with the parent chain’s signal.