There was a window of time (generally, the 1970's) when arguably the best combination of materials for a lively, small wave hull was a mix of Superlight Clark Foam, 4oz Volan cloth, Dion resin, and a small balsa stringer. All finished off with a hot coat sanded down to 320 grit wet and dry.
The upside was multi-fold. From a builder's perspective, a blank with a small balsa stringer was easier to control during the shaping process (when compared to a stringerless blank.) It was more stable, and there was a defined centerline to work from, visually. The shaped blank was also less apt to sag or warp during the glassing process.
The balsa stringer/light cloth combination was, if anything, more flexible than pure stringerless with heavier cloth. With a small balsa stringer, the blank was a bit stiffer, but the lighter cloth allowed for more flex. There was a close balance between the stiffness generated by the blank and the stiffness generated by the cloth. (A stringerless board was a small step in the direction of "all shell and no core.")
The downside was deck durability. In order to yield the flex of a stringerless hull with 6oz cloth, a single layer of 4oz (with a 4oz deck patch) was needed. And that lead to a deck that was vulnerable to the slightest pressure. (Dirt used to call them "throwaway surfboards.")
GL with a 4oz, balsa stringer hull, 1976.
The hull pictured at the top appears to be one of the later versions of these boards. The white fin box and leash loop date it around 1980. (Just a guess.)
By the mid-80's, enough changed in the available materials that the 4oz/balsa combination wasn't as effective. The crisp, firm Superlight Clark foam blanks weakened, as did the resin compounds. (Both due to legitimate environmental concerns.) A single layer of 4oz cloth was no longer enough to hold a flexible board together.
One practical takeaway from all this: Regardless of the glassing schedule, small balsa stringers are a design-hack not enough of today's hull builders take advantage of.