Correct. Cutting Treble and Bass will give you a mid boosted tone but with reduced output. The volume needs to be adjusted to bring it back up to level. This is why I associate that knob with mids.
However you want to look at it, this pedal is capable of creating mid-heavy tones, but many users might miss this functionality if they don't consider the volume knob's role in shaping the sound. Understanding how the volume knob interacts with the tone knobs can help avoid disappointment for those who struggle to dial in the desired sound initially.