The Thieves Guild questline is also made substantially worse by a 25 year gap in the backstory.
Like DAMN Karliah, you were working on this revenge plan for 25 years and this is all you have? A stupid mead business scheme and one single dose of the poison everything hinges on?
Of course, the fact that the writers keep patting themselves on the back by having every other character comment on how genius her plan is doesn’t help
If you’re interested in something fun, there’s an old blog post about how terrible the Thieves Guild questline is:
https://www.shamusyoung.com/twentysidedtale/?p=14422
It’s a bit long, but I think it’s very entertaining. Deep dive into every single plot hole, and nonsensical story beat.