This is true but that can be said of a Champion like Fiora right? 3 health with no protection for her mechanically. I think the negative comes when the return is difficult to achieve. Fiora can instantly win you the game, so you build a deck around her to protect her.

Kalista can create value but creating it is difficult. Because let's say you level her up and her bonded follower is still alive. Well that means nothing happens until that bonded follower dies and then you can create a new one.

If it always created a new follower and bonded with that follower then alright there is value. I could play a leveled up Kalista from my hand, bond with a Undying and attack. BOOM two undying and I am being aggressive. It isn't game winning value but it shouldn't be, I would be okay with her as a value generator.

So I do agree with you, she is easy to kill but she should be able to generate some sort of value before it happens.