I have 10 tanks, all densely planted, with a soil under gravel or sand substrate. The Hygrophila is growing well in all of them except the one with the bristlenoses. I don't use CO2 or fertilisers in any of them but all the plants grow well without, I reckon the fish produce enough of both, all tanks have a decent load of fish, up to full capacity.
I first thought they were just eating algae of the leaves until I saw the leaves disappearing before my eyes. They do clean algae off the Java fern, but don't touch the leaves. I weighed down a piece of unblanched soft (butterhead) lettuce to the tank bottom and they soon ate that. So I reckon they do eat some plants, but only the softest ones.
I have a big piece of bogwood in their tank, it's almost the length of the tank.
When I got them, they had been kept by the previous owners in a small tank with nothing but plastic plants and "ornaments". The advert had said "albino catfish" and I assumed they would be Corydoras so was surprised to see what they were. When I put them in my tank, they found the bogwood in seconds and immediately clamped on and started chomping on it and stayed there for several hours. They are about twice the size they were when I got them so are clearly doing OK. The other plants in the tank have grown and spread to fill up the space.