There are plenty of ways to lose fish, even with water changes. But you're much more likely to lose fish due to a lack of them.
Like your dad said, heavily planted tanks don't require them as often, but they are still required. There is no system known to man that completely alleviates the need to perform water changes.
Clear water doesn't mean healthy water. You can use a UV sterilizer, chemicals, filtration, etc. to make your water clear, but it can still be full of disease or parasites, just as it can contain dangerously high levels of toxins in the water.
There's a difference between "tests are low", "levels are ok", "levels are safe", and the only truly safe readings; ZERO ammonia, and ZERO nitrite. "Low" readings potentially mean more than zero, and if there's any more than zero, it's dangerous to your fish.