Once you go duck...
It does make it slightly harder to carve and pressure the edge than riding with forward angles. (That is a controversial statement, but imo correct.) If carving were everything, we'd all be on Skwaals; and if carving meant nothing, we'd all go without highbacks, and we all know how fun that is, right?
There's definitely no less ability to "pressure the edge" and really pressure comes from the snow/board contact, not me pushing or whatever on the board. So the tilt (edge angle), speed and snow surface create the pressure that I feel and try to manage, regulate or redirect as the case may be. Stance angles may have an effect on the last statement, but not on the factors creating pressure. I'd say angles that don't match one's anatomy would create the issue, more than directional v. duck. I have no problem from stance in managing, regulating or redirecting pressure during turns.
Current set up: regular stance, 15 front foot, -12 rear foot. I've tooled around with slightly more (18) on the front and slightly less (-9) on the rear, but will start out the year with the current set up. I used to ride like 32 front and 18 rear, but couldn't ride as aggressively as I do now going switch. Way back in the day, I originally started off at 21 front foot and like 9 rear (to match Terje or something).
The comments on matching one's anatomy are right on. The sitting on the edge of a table is a reasonably effective tool to get someone started. I'm not a doctor, so not sure about the higher stress on the knees deal. I've seen someone (with previous knee issues) ride duck (and enjoy it more=ride better), but have knee pain, and others ride duck and have no pain whatsoever.