The potency in the spell description is just part of the healing algorithm (that I would not be able to iterate for you). To give you an example, my healing magic potency (Solo) as SCH is 412. Adloquium potency is 300. I cure for roughly 610hp. Succor's potency is 150 with the same solo healing potency, and heals almost exactly 300hp. Half spell potency, half the result. I would imagine Medica with my healing potency would land roughly around 500.

The description is right, you just confused Succor and Adloquium.