No, no don't discard and call it a day! It's not that bad; it's not even near dead, although it may look so. Remember gardeners don't give up, we re-root, even if it means starting again. We've all lost specimens before we got the hang of our plants.

That's learning, a normal part of gardening.
Jungle cacti are not finicky, they just require different conditions from desert cacti. They are succulents and should be treated as such. If it were mine, I'd check the roots condition and repot accordingly. Remember that in potting media, particles break down and become smaller over time. There are less air holes for the roots to breathe and in time they suffocate and slowly die. That's why it's important to repot yearly, especially if you're using a peatty mix. You have a fairly large specimen to experiment with, so do so.