because the few battles that involves Iranian faction as one side of the conflict is those that was a defeat for them. not even one battle with Iranian side to be victor (Not just Sassanids even one battle regarding Achaemenids was again a defeat for them). This of course follows the same attitude of glorifying west that exists in all other medias (youtube or not) so nothing especial about this channel !
Edit : the first time I discovered this channel was yesterday through recommendation that was a video about Battle of Al-Qadisiyyah which was actually a re-telling of same fairytale that muslim invaders said about their Campaign against Sassanid Iranshar. (looks like Arabs are as good as greeks in making up stories and sell them as facts !)