Yeah, I guess it would make the water too soft. That's why your LaPerla has the Tab function, which deactivates the softener and minimizes rinse aid dosing.
I once saw the cycle progress chart for Bosch/Siemens dishwashers (Euro versions) and it showed that, with activated 3in1 function, the dishwasher will only do one interim rinse with a low water level (to maximize the carry-over effect) and raise the final rinse temperature by 3°C. I'm all for separate products, too.