That's correct in my experience. Galvanic corrosion was never a problem for the capacitive sensors I developed a few years back (unlike the resistive sensors linked by the parent). However you typically want them more rugged than a bare PCB for industrial settings and since the capacitive field can pass through plastic I had them in a plastic housing filled with resin. Perfectly isolated from the outside environment and hard as a rock.

Here's a prototype: https://imgur.com/9yO28CY