I’m confident saying that you gave them both great cat lives and they were lucky to be yours.
Although of course you sign up for this when you get a pet that’s not a tortoise or something, and I’ve heard people say that they don’t want pets because they don’t want to go through that type of loss, I think having pets adds something important to your life (if you’re the type) and is worth it.
What you said also reminds me of a scene that’s been haunting me, when the cat I lost last week looked up at me and around the room in her last moments with her one good eye, reminding me that almost everything about her life was my responsibility, including when it ended. It’s hard to be comfortable with that even if you know you’re doing the right thing.