While the deep sand bed can export nitrogen compounds, the CUC really just recycles organics. They are best at retrieving small bits of food from the rocks and sand where it can get caught and decompose. But they don't reduce organic loads at all. Fun to watch.
While the deep,sand bed is a tried and true technology, it doesn't fit everyone's system, similar to algae turf scrubbing. The tried and true live rock with skimming and water exchanges method is by far the most common way to build a successful reef. Phosphates can be reduced by controlling feeding, using RO
water exclusively and if still high, add some GFO
or Phosguard to the sump in a mesh bag.