That's a good one...
Defining a muffler's performance by the loudness is not our way of developping exhaust, if it was, we'd all be running straight pipes. Our approach to exhaust development seems to have shown great results as we are the biggest exhaust manufacturer in the world.
Obviously if loud was your goal, we are not for you.
In terms of performance, all our exhaust are straight through mufflers and most of them are dyno tested with great gains.
You could have simply said they are quiet exhaust...not "bad overall".
Your examples are mostly flawed, all of them were using our universals, which are just that, universals.
Old chevys, nissan maximas, lexus, mazda, none of those are our primary markets and we don't have specific exhausts for the ones you listed.
There's much more to the muffler that makes a car sound good or bad.