I'm a malaysian and I've been keeping channa since 1985, 99.9% of large channa keepers here do it this way the 0.1% is probably that friend of yours, so you're trying to say you know better?
Keeping large channa in tropical climate with close top plus all the lightings will raise the water temperature to 30-32ºC.
It is never a good idea keeping large channa with substrate, plus you're suggesting deep substrate, if you say other wise it shows how shallow your knowledge on monster fish.
If you say your fish is fine, then they will definitely do better without the substrate.
Please dun torture your fish.