I've talked about this before with my friends, but I don't think I can ever genuinely get over how wasted material Kate ended up being.
Like, don't get me wrong, I'm not saying she needs to have a major role or has to be Omni-Man level of importance, but there was SO much she could have been with her relationships with others that didn't (ever) involve Immortal or "breaking up" a relationship (I'll only defend her on that; Rex lied to her about him and Eve. At least he got a redemption).
Kate has a similar past to both Eve and Rex, HER TEAMMATES; troubled family and grew up in a government agency as a potential soldier/hero in the future. Her brother couldn't handle that anymore, so he left and became an assassin, which I feel like the show hasn't really explored how she really feels about that all too well besides the forgettable prison scene talk she had with Paul. I understand why she was closed off, and why she may view relationships differently with others, BUT that also led to so much potential of her past troubling her even into adulthood and development with her friends (both old and new). They even could have showed her spawning in so many clones like Paul has, yes I know it can be painful for her but we could have seen she's willing to push to her limits if it meant protecting people and her friends/found family.
Instead, they limit to how powerful she could be and gave it to Paul instead (which is bullshit ngl, she should have a moment to shine), then reduced her as "Immortal's gf/wife" and basically nothing more. That's what is jarring to me - they made her change personality and opinions for a mid man she only knew for a short while compared to people she's known for literal years. It wasn't like "after she became a guardian she started to view things differently" type deal, it was more she got with Immortal and her personality just completely changed (even though she already lacks it because the writers couldn't bother with her).
I don't like Kate, both show and comics, but I really grieve what she could have been if the writers developed her relationships, powers, and hardships more instead of bitchy personality that no one likes to watch on screen (if Kate fans are reading this I apologize, I just wished she was handled better by the writers).