Hello BBm'ers,
I use several kinds of set ups for my discus depending on whether breeding or rearing.
1. BB
2. <1/4 inch of substrate
3. Planted breeder grow out. 1/3 of the back has 3" deep sustrate confined within a 3" high siliconed glass box with front 2/3 barely covered with a sprinkling of substrate but essentially bare. It's easy to hydrovac the back, and make it livingroom worthy. I have a massive DIY wet/dry in these planted tanks. 10 discus grew from 2-1/2 in to 6+ in. in 10 months and have paired and moved to bare 20H's. Replaced them with 10 Heckels. I feed growing breeders 4 to 6 X day. Tank is 75g plus 25 more in the sump. 900gph return flow. There are as many approaches as there are aquarists. Do what works best for you. Discus are happy in any clean water changed regularly,kept warm and fed well. They're quick to let you know if WQ has slipped too much.
I am in total agreement that as a general rule that a fully covered bottom leads eventually WQ problems. It's doable but generally not if you have many tanks to keep up, especially if discus are your main interest as they are for me.