The "stiffening effect" effect of tied and soldered spokes might have been much more noticeable back in the days of very light aluminum rims (Scheerens, Nisi, others), wooden rims, and in general much lower spoke tensions.
The soldering also might have gripped the older non-stainless spokes enough to change the "feel" to the rider and the lifespan of the wheel ?
Also BITD most spokes were not as reliable as today, and so there was more of a possibility of having a loose / broken spoke in a race, or on a loaded touring bike.

Jobst was using modern Wheelsmith wheels with the more accepted modern idea of higher spoke tension @90-110kg/f. Think about what the TOTAL tension is on those modern wheels. It would be an interesting comparison if he had also tried it on old equipment.

The only times I've seen the spokes create a "notch" at the final crossing is on truly old, crapped-out and very low tensioned wheels.

Finally - the unsoldered ties on the pictured wheel, especially with the little vestigial piece of wire just hanging out there, looks truly TERRIBLE.
A good T&S job looks much better than that. I actually like the look of a good T&S even if it does nothing structurally. YMMV.