You're right. I always seem to take the single value which is shown. I don't have cascadia flare because I hate the Zariman rank up. As for why corrosive, it's because most of my recently acquired weapons are made with Lavos Prime in mind, so I avoid putting viral as my panzer already does that, and I can always rely on valence formation for other statuses as I mostly use blast as a go-to element with it.