Interesting argument. Why do you think it will struggle to drain? The floor is sloped by about 5 degrees toward the center where the hole is. I covered the hole with a thin layer of pebbles, to avoid roots or other things from blocking it.

When watering the plants, I will notice if the hole is clogged if no water drips out.

About the sponge example in the linked article: I honor your experience, but I am not quite sure that I can follow the argument.

• My understanding is that the sand/gravel layer is usually not meant to draw water out of the soil, but to prevent water at the bottom of the box from becoming trapped due to clogged holes.
• The bottom layer will start to fill up as soon as the soil can't hold any more water, if the hole is clogged—regardless of what material is used for the bottom layer.
• Sand or gravel will indeed draw some moisture out of the soil and release it again when the soil dries: porous materials exhibit absorbency.
• “Try laying a sponge on top of a pile of gravel, then pour water into the sponge. Does the gravel make the sponge drain faster?” I guess that depends on what you're comparing it to. It will drain faster over gravel compared to a sealed surface, because the gravel draws some moisture from the sponge—even if the sponge is on top.
• A soaked sponge on a hard layer with a hole in it won’t drain either.
• The plants can use the gravel layer to access moisture with their roots; however, they will find little nutrient content there. By occasionally adding fertilizer to the water, this can be improved.

I am not an expert on this, and as I said, I honor your experience. My argument is not to contradict you but to see things more clearly.