Not the whole story though. Baker potatoes like russets are high in starch, purple potatoes like Viking or a Red Bliss type are much higher in protein, while reds, yellows, and such are in between. Your waxier potatoes are much lower glycemic than the starchier ones.
Also note that it's carbs, not salt, that has a greater and longer term effect on blood pressure, so yes eating starchy potatoes that much, or any kind of carb, is going to do that.