He could have finished off Aizen without Suicide. He had Aizen in his grip, nothing would have stopped him from cutting Aizen to pieces right there and then. And that's not the point, point is, there are ways to counter KS, its not unbeatable like you make it out to be. Yamamoto's way is just one way to do it.
When have I ever assumed this? Breaking out of Genjutsu in Naruto either requires the character to have sufficient expertise in the area or have an outside party flow chakra through them. In Bleach, its been proven that having enough Reiatsu difference between the character and the attack nullifies the attack, Bambietta going Volstandig against Shinji's Shikai to nullify it or Cang Du going Volstandig to nullify Hitsugaya's Bankai are just some of the many examples of this.
Why don't you accept portrayal? Yes, Gremmy has limits, but nullifying Aizens Shikai is not outside of his imagination boundaries if dropping a meteor is within it. And what would hypnosis do exactly? Royd simply uses the same method that Yamamoto used to break out. Or he uses his Quincy Spell and take Aizen down without having to actually see him.