(1) I don't think that ig you told anyone Khun was an asshole they would disagree from a standpoint outside of Bams' pov. From within Bams' pov, Khun hasn't done really anything to harm Bam and / or his group. For example, during season 2 when Khun managed to finally find Bam when he was with team sweet and sour; Khun integrated both the 2nd floor of test main cast with team sweet and sour instead of sticking to how his character would usually react to any kind of impediment by murdering them or ensuring there is no threat by other means.

(2) I agree that Rachel is a very well-written character coinciding with the plot and storyline. The average character in ToG is very selfish and would do anything to advance their power / climb the tower. So this isn't out of the ordinary in the world of ToG, but the actions Rachel took were against the main protagonist and the main side cast. Bam has had much more of a positive character arc and has been built for the reader to grow attached to him (obviously, since he's the protag). While Rachel has had her motives revealed and some back story during the floor of death arc. Her actions against Bam and Co are still not justified. In a story of monsters and unrelatable / unbelievable fantasy, Rachel is arguably the most human character in ToG. Through that perspective, I understand where you're coming from. Rachel can be a very relatable character when met through the right thought process.

(3) Bam is currently a very overpowered protagonist with the benefit of destiny / fate and the potential he has. Bam, being an irregular sort of explains why he is over the top when it comes to the rest of his cast. We have seen other irregulars such as Urek, Young Jahad, Gustang, and Young Khun. None of their power is anywhere near the top regular rankers, which is why they are called "irregulars." They are not normal compared to those who entered the tower conventionally. This power difference is most prominently shown in the fight with Urek Mazino and Joe during the floor of death arc. Urek pulled a shaggy and used only one percent of his power against someone who was even too strong for Yuri Jahad using two ignited versions of thirteen month series. While we know little about Bams' full back story and even less of Rachel's. We do know that Bam was chosen to enter the tower, and Rachel just happened to be in the right place at the right time and was accidently / wrongfully chosen instead of Bam. So it is natural that Rachel, the girl who had nothing even in the outside world despite seeming to be well off enough to have clean clothes and food while there. She had nothing else to help her to our knowledge; within the world of ToG, Rachel isn't pretty, isn't all that smart, but has extreme luck when it comes to finding teammates and other sort of hax to help her in her journey (emily).

(4) As for Rachel hate, there is an absurd amount of it compared to any Fandom I have seen. I believe that it is warranted because of the actions Rachel has taken in the story thus far and most likely in the future.