The one aspect of a slow cooker that would be nearly impossible to reproduce with an induction element is the area being cooked.
While cast iron will conduct heat, a slow cooker is a two-part device, an inner cooking vessel and an outer 'pot' with a heating element in the base. The hard part to reproduce is the air space between them. It means stuff doesn't burn to the bottom, doesn't need stirring, and the cooking vessel is heated right up the sides nearly to the rim.
This means the food is cooked on all sides, even the top by means of the steam above the food.
That's why they say it adds 20 minutes to the cooking time for each time you lift the lid, the steam escapes and that heat is lost.