Do you believe that tough and harsh training will have better results than slow and moderate training? Why?

It's not about tough or slow training, it's about training correct so you can feel that you have work for something and your body part will feel that, that you have given your 100% , never repeat same exercise every week. And the main part is diet if your diet is not good then your hard training is also not worthy

If you mean with higher resistance/Load (by tough and harsh) and moderate or low load. The idea of training is to cause the microtrauma of the muscle finres (wear and tear or breaking down of muscle fibres) . Lets suppose you need to break 10 pencils (muscles), you can break it in many way...Example -if you have the strength you can break them all together or in two sets of 5 or one by one, similar is the case with breaking the muscles. Whether you cause the required microtrauma with high load in short period of time or with light load in longer period of time. You need to break the muscle to grow and make it stronger with your nutrition and rest. The advantage of heavy weight lifting is that you gain more strength over shorter period of time but the most important thing is to lift safe than ego lifting! Train insane but safety first!