You should add Frost Queen's claim as the first item. It's completely broken in its current state: Super cheap, decent stats, insane active + passive that has given you 2000+ gold lategame!
Also, Ludens Echo counts in thunderlords, allowing you to 2 shot squishies if you're fed enough. I prefer to rush frost queens into ludens at this point. Xerath is actually very viable at the moment.

Thank you for the suggestions! I added a few.

You might want to talk about alternative summoner spells. I suppose that Cleanse would make a viable choice in many games for instance.
I'd put the chapter 'Pros and Cons' right after the introduction as it informs the reader about the most important basic facts.
You should clarify item build paths when playing against AD / AP and from behind - simply expand the content concerning items.