That's the usual way to use a sump for the drain discharge. To go into the line from the sump pump would mean it would have to have a check valve in it or the water would want to run downhill into the pump and sump. If there were a check valve, then the drain water would have to be capable of going up the line and then outside wherever and the discharge water can only go up from the control valve on the filter a few feet; usually not more than 5-6'. If you put it into the pump line, every time the sump pump came on it would pressurize the control valve drain line back to the control valve... thta's not good.
Any restriction in the free flow of the drain water causes insufficient backwashing of the filter mineral/media which then causes the filter to fail. So no check valve in the filter/softener drain line. So does less often backwashes as opposed to more frequent backwashing. So don't go changing the schedule unless you want to assume the risk of that. Us filter/softener guys don't just pick numbers or frequency out of our ear, the frequency depends on what and how much of it is to be filtered and then how many gallons of water can be treated before a backwash (or regeneration) is required. That normally depends on the number of people in the household.
Also, a septic system that is operating correctly, will have no problem with the supposed "extra" (wasted!) water. The filter is making bad water good, so how's that wasting water? So says the latest and repeated EPA research on softeners specifically. Actually, all 3-4 studies of the subject have said the same thing....
Gary Quality Water Associates