Obviously a comment from synthetic nutrient grower, the solution provided to grow without wet compost is impossible to do and have active soil web. Fungus gnats are an affirmation the grower their organic soil web is alive and well. They don't have fungus gnats because they poor crap in their soil which is used more as a medium to hold plant in container and absorb synthetic nutrients then it is too feed them using the soil as a biological web to properly feed the plants.
All true organic growers have to prepare to deal with fungus gnats if your going to have great active organic soil. Just know fungus gnat will always be something to treat your soil for because if it is alive and well it will attract them. Just put out the not welcome sign with the neem or hydrogen peroxide and you will be just fine and your plants will be too.
DankSwag