Think about it this way: For cardio I bet you run at a somewhat slow pace and pound out a few miles at a time. This is a decent way to lose weight, but you will end up burning away muscle too. It is somewhat counterproductive. What you want to do is run sprints…full out sprints for about 20 seconds and them walk/jog till you catch your breath. Repeat this 10 times. This will focus on burning fat only and help you keep and build more muscle. This is a little extreem but it will help get the point across. Look at a marathon runner’s build …not too impressive…lean but not too impressive…then look at a sprinter’s body typically lean and a lot of muscle.
As for the light weight gets you toned…not really. Sure different rep ranges are better for hyopothy…but high reps with light weights doesnt mean it will give you a toned look. Diet and losing fat will. You want to build as much muscle as possible…and there are many ways do do it…including different rep ranges.