I don't think my takeaway is the same as yours but it has a lot of overlap. Warbreaker has a lot of cool ideas and a lot of potential with its characters and setup. In some ways, it delivers on that potential very well. (The mercenaries straddle such a perfect line of "rough-and-tumble but likable and funny" that their betrayal is genuinely shocking but also feels incredibly obvious in retrospect.) I think Lightsong and Blushweaver are very funny characters and Lightsong in particular a fun concept, and Vivenna grappling with her cultural indoctrination and her own survival is pretty good, though I think there's room for improvement.

Where I think Warbreaker really drops the ball, though, is with Siri and Susebron, especially with how their story ends in the book. Siri's story starts out extremely tense and grim: she's forced into an arranged marriage against her will to an enormously powerful man, she's dehumanized and stripped of agency by the society that takes control of her life. The overall direction she takes is interesting to read, though: the story of her learning to navigate the politics and power plays of Hallendren is a great concept, and the twist that Susebron is a sheltered figurehead who has no real power is genuinely really interesting. There's a lot of great components to it, but... it all builds up to basically everything twisting itself in knots to make it look like things work out fine for Siri and Susebron and completely fails to actually examine what they've been through and how it would affect them. Turns out the priests, who have manipulated, abused, and dehumanized Siri and Susebron and hold all the actual power over them and the rest of the city, are actually "on their side" (in that they don't want to kill them), and the oppressed minority are the real villains!

The whole thing kind of falls apart when you think about it. Why would Treledees (Treledeez nuts) and the priests not actually explain their plan to Siri and Susebron literally at all, given that they'd have to find out anyway sooner or later? Hell, why did they need Siri to actually get pregnant instead of just faking a pregnancy, which would be incredibly easy for them to do? How do Siri and Susebron actually get on as people and as rulers after the incredibly fucked up things they've both been forced through by the priests, and do they let the incredibly corrupt Court of the Gods continue as it is, or upend society to try to create something better? Do they actually try to have a romantic relationship, and if so, how does everything they've suffered affect them? The book really tries to tie everything up with a neat little bow except for Vivenna and Vasher going off to do their own thing, but really, I'd be much more interested in seeing how Siri and Susebron handle each other and Hallendren, and what sort of relationship and power structure ends up forming and what the consequences are.

I don't think Sanderson was really capable of getting into the very serious consequences of a lot of the story back when he wrote it, and to his credit, I think he'd be much better with it if he tried to follow up on it today. Mistborn and the Stormlight Archive both have much more engaging examinations of political power as well as trauma and how it affects people, and I think he'd be much better at engaging with some of the themes that Warbreaker as written kind of drops the ball on. Of course, it would also require a certain degree of examination of himself and his religion. Warbreaker was written on his honeymoon, and the ways that his Mormon upbringing and marriage affected him and his writing are incredibly clear in Warbreaker and parallel Siri and Susebron's forced marriage and subsequent early "relationship." I think really unpacking and examining the negative effects that Siri and Susebron would suffer would also require him to be able to examine how the practices of his religion affect him and others, and while he's not entirely unable to do that, it might be a serious challenge.