Regarding an 8bit down counter

And don't put too much emphasis on the RTL viewer. I'm not even sure if it has a "counter" block. It may look like an adder(since a counter is just an adder with a constant of 1 on one side). The main concern is that after the RTL gets synthesized, what does it look like? You'll want to use the Technology Map View for this. It's much more difficult to read, since it's at a lower level. The other thing to look at is the resource usage, which is really the most important thing. If your 8-bit counter uses 8 logic elements(or something different dependint on the family you're targeting), than that's as compact as it gets. Whether the RTL viewer shows you an adder and a mux, or a counter, is just an intermediate step.