There can still be progression: the torsional rigidity isn't set to be that of a stock race ski.
We skied 0 base 0 side on straight skis just fine because the tips and tails had low torsional rigidity limits.
Hence the subsequent point of lateral camber and preload for the hypothetical megafat railed setup.
How do you keep a very wide tip torsionally rigid? New materials and construction techniques. This is why it is now possible to have wider skis that are torsionally stiff. Early wide skis suffered from lack of torsionally rigidity and the manufacturers had a much more difficult time separating torsional rigidity from longitudinally rigidity. Mnay skis that were torsionally rigid were also longitudianlly stiff. or vice versa.
The reason we bevel now is the shape of the ski!!! Not the torsional rigidity.
Wide tips and tails with no base bevel do not make a user friendly ski.
the old skis had tips and (and some time tails narrower then the waist. But also that old 90 degree edge was not progressive back in the day. they were pretty much on or off. You don't remember check turns??? or check hops!
Or stepping uphill to make it through the gates, because you really couldn't just roll the ski on edge at the top of the turn?