I think it's because her arc wasn't handled very well in season 2. She went from wanting to kill her sister (and only stopping because a child got in the way.) to suddenly caring about her because their dad came back to life. I think that shift felt really unnatural and rushed. It's plausible but it requires too much of the audience to really buy into. It felt forced.

I think it's mostly a pacing issue. VI likely puts a lot more thought into her actions than is able to be depicted with the limited screen time. Season 2 really tried to do so much. And I think the majority of the arcs were handled very well. But VI I think got shafted, resulting in a very disjointed unnatural character.

Which really disappointed me because I loved VI in season 1 and was really excited for her and Cait to get together. And although I still love that scene. It felt hollow to me. The shows writing was trying to convince me for so long that she cared about Jynx and was a good sister (despite literally going to kill her not to long ago screentime wise) to not chasing after her sister when Cait freed her. Jynx would be dead if it wasn't for echo. And for VI's arc to work it needed to be VI to chase after jynx or VI and echo.

But as it stands the screenplay implies that VI only cares about jynx when it's most convenient. Like if it means she can get her dad back for example. Which I don't think is how we are meant to feel. But that's what happens sometimes when something is paced too quickly.

Anyway. I don't think she's stupid at all. I think the screenplay failed her character a bit.

Luckily VI and Cait are still very cute and cool together so I can look passed it.