Homo erectus was built much differently than neanderthal because erectus lived in a different environment. Having evolved directly in Africa and then moving towards Asia, erectus was built for speed nd a hot environment.Consuming more protein in general, does not at all enhance growth, for processing more protein requires extra vitamins and energy. Logically, Neanderthals consuming much more animal food ,were less tall than earlier Homo erectus, who consumed less animal food and more fruits.
Homo neanderthal, however, was in Europe durng the ICE AGE. So being short and stocky helped him to retain body heat. Neanderthal did not have advanced sewing practices, which would have made any skin clothes he wore for the most part ineffective. The skins found near neanderthal sites were used mostly for bedding.
Also, lack of height was in no way a problem for neanderthal, because he was obviously NOT lacking in vitamins and nutrients, and suffered very few deficiencies as that quoted text would have readers believe. Neanderthal had bones 25% more denser thant he most ardent body-builders of today. Yes that's right; neanderthal's bones were 25% denser, thicker, and sturdier than Sylvester Stallone or Mr. Universe. They were probably just as strong, but with smaller sized, denser muscles. THey had much larger joints, allowing for more connectivie tissues. Their hands were larger, and their forarms and forlegs were much shorter and more densly packed with muscles and tendons. Neanderthal's jaw was also thicker and more robust. His skull was thicker, and he had a larger brain. His structure was built for power, and it is postulated that he was capable of great acceleration, speed, feats of strength, and climbing. He was the Superman of human evolution.
Truth be told, if a modern human met up with a neanderthal and the two got into a fight, the modern human wouldn't have a chance in heck. Neanderthal was that well evolved and developed. Sadly we has adapted for an ice-age which was on it's way out. There is no evidence modern humans killed him off our replaced him. No one knows why neanderthal became extinct.