I completely understand why you guys are upset and calling this "sexism," but as a woman myself, please let me kindly explain to you why this act is justified.
First of all, it is only 1 hour and 30 minutes of women and non-binary people only, and then afterwards everyone else can join. Let me repeat that. _It is only 1 hour and 30 minutes in which men aren't included_ -- is it really THAT BIG of a problem to you guys that the least represented group in this community gets 1 hour and 30 minutes to themselves?
Think of it like this: We all know that cisgender men are the biggest group in the community of in League of Legends. Women and non-binary folk are at the very bottom of the community, often underrepresented and outspoken by their male counterparts. So, it's only reasonable and fair to give this minority and outspoken group a window to be able to be a part of a discussion without being overshadowed by the majority. This is a direct counterargument to everyone saying "just let everyone be included" -- that "everyone" includes a large majority of people that can easily, and very well unintentionally, overshadow the smaller groups in the community. This is why women and non-binary people are given this opportunity to shine.
I hope you guys take the time to think about my reasoning rather than responding with anger and hate. I am explaining to you all why I, as a woman, agree with this move. Maybe other women and non-binary people disagree with me, that's okay. But this is me explaining the reasoning behind riot's decision. Thank you.