Symbology created with geometry generators renders murky in print legend

Question

I have a style that makes use of the geometry generator for a wavy line:

the code is as follows, with units set to mm

wave($geometry,
    6,
    1.5)
    )

When I export the map as a vector format (PDF/SVG), the legend gets very murky:

Exporting as Raster works fine:

I played around with the settings for PDF export, to no avail. But I realized, this is scale dependent:

Is there any fix? Is it possible to mimik another scale for the legend than for the map? Or should I use SVG's to style my layers?