My antique Kästle SGs are a torsionally rigid as any modern ski I have skied.
If you were skiing a stiff ski you had to pressure the tips to get them to bend, and the start the cut from the tip and follow through. If you were too light for the length, because you needed the extra length for stability at speed, you got good at skiing one ski at a time until up to speed, and yes, some dynamic loading did help at times.
I have to agree. My straight Kastle Combi's feel just as torsionally rigid to me as my shaped Kastle RX 12's -- but that's what both were designed for: aggressive gate skiing... And both demand weighting the tip and, if you sit back on them, enjoy the ride -- wherever it may decide to take you! (the straight skis more than the shaped skis).
Both of them like aggressive fast skiing and the faster you go the smoother they feel and the better they respond...