> The renderer isn't helping here, as it's arbitrarily making regular roads look hollow and without a surface area.

https://wiki.openstreetmap.org/wiki/Tagging_for_the_renderer - incorrect tagging is not acceptable just because in one specific render it looks OK

> Isn't the area really refering to the exterior of the road?

area:highway is doing that - and someone removed it and replaced with incorrect highway=service+area=yes