We have different POV about Lord Fluffy's childhood, don't we. I tend to follow Movie 3 since RT was a consultant on that picture. For me his Fluffyiness was raised as a lord's son. He was an adult in the prime of life when Daddy died and he expected that he would receive all of Daddy's toys. Inupapa and SessMom were still together. Inupapa left her a lot to tell Sessy which does not imply a breakup from his relationship with Izayoi. I do not think that Izayoi was ever allowed in his palace. I view SessMom as the chief wife and Izayoi as more of concubine. Having a wife and concubines was not surprising in 16th century Japan. Tokugawa had 19 wifes and concubines. I see nothing to indicate that Inupapa was a hardass only that Sesshy did not get the inheritance he was expecting to make him more powerful. I was looking at the manga Chapter 15 where he is about to pull Tessaiga. He feels that it will make him a much more powerful being. Totsai tells Sesshy that it was Tessaiga not Inuyasha that took it upon itself to punish Sesshy for trying to steal something that did not belong to it. RT only tells us that the dragon dealt the fateful wound. The movie says he went to save mother and son.

I do not think that RT ever thought of Sesshy as evil. He had some lessons to learn before he could become a dai-youaki just as Inuyasha had find a way to ignite the sword, smell the windscar and the Backlash Wave. If anything Inupapa is trying to show them that nothing comes easy in this life. If Sesshoumaru had never been blasted by the Windscar, he would never have found Rin which was one of the most important lessons in his life.