Don’t think it’s a case that it would be too rough for them however they would be used to a sand substrate. I imagine they would have to work harder to get to food whereas on sand it tends to sit on the top. I am a massive cory lover, so I have to say I always prefer seeing them on something more natural. No doubt someone else will come along and say some are used to a soil base 😂. Nothing would surprise me in nature, and I’m no expert.