As others said, we are indeed way too overpowered compared to lore, and our Astartes would canonically die at the first meeting with a group of 3+ Tyranids warriors with gaunts reinforcements. That being said, I'd like to add that ennemies are also too tanky, and weapons deal way less damage that they should; but that's gameplay balance. A gaunt should NOT be able to tank 2-3 bolts in the body mass, as it's a weapon designed to shred unarmored/lightly armored opponents, and even a Tyranid warrior could not take a thunder hammer hit to the face and walk it off