I think I have a bit different view on this subject than most.
First of all I don't believe that the arch of the foot should be a load bearing surface. Most of the pressure should be on the ball and heel.
To lock the foot so that you cannot pronate and supinate is IMO a big no-no. You loose a large part of fine balancing abilities.
The type of foot-bed that Atomicaman refers to, e.g. conformable, is fine, because they take only minimal weight at the arch, but a rigid foot bed is not good.
I know first hand that the top skiers in Sweden have all moved away from rigid.
If you over-pronate there might be a reason to adjust, but IMO the real culprit is often non-neutral feet and/or collapsing arches due to wearing bad shoes. What you need is mobility and correct movement mechanics.
Can you tip your foot to the LTE without lifting the BTE? Can you pressure the first metatarsel at will without collapsing the arch? If not you have lost your movement abilities in the foot.
This is how the subtalar joint in the ankle works:
In other words tipping the foot is translated into long axis rotation around an axis similar to the tibia. This means the knee rotates around this axis and if it is bend it also moves laterally.
This further means that tipping the foot is not just about tipping the boot the same amount.
We are not talking about moving the knee a lot when we tip the feet. Knee-angulation in WC skiers is usually less than 4-5 degrees during the pressure phase. Just enough to align the knee slightly inside the force that stems from the side of the foot when you tip it. If the knee is slightly outside instead you will likely suffer from e.g. chatter and you need some compensation.
Another interesting aspect is where is the center of the subtalar joint is in respect to the forces? If it is aligned skiing will be very effective, but if it is not your lower legs muscles will work overtime to compensate and you might even feel better if you immobilize the joint to give some relief, but it is a band-aid.
David McPhail has written virtually hundreds of blog posts on these matters, and although I don't like all of them there is tons of food for thought in his posts.