It's a really important component. Between its stats, killers, and unbindability it's a pretty good card to have. That said you can probably get away without one depending on your other subs. Spica fills the God killer hole well enough and Star Justice covers unbindability. If you're running the lead switch side you can possibly get away with no Rag Dragon since ideally you aren't trying to make the kill shot on Kali. If you want to try let me know. Just bring a Kotodama (or similar) with an orb change inherit.
Here's a
Video showing the "template" Arena farm team complete with sopdet spawn. To me as long as one player is capable of killing the major threats and you have a panic heal button things should be ok.
EDIT:
Ok so lets talk about what Machine Athena can do outside quick farming Arena
Given her multiplier matches up with Mhera anything she can do Mathena can do as well assuming qualifying subs. Mhera AFAIK can farm all rogues, MZeus, and any "normal" content with minimal prep. Given her relative ease to acquire (compared to say MZeus) I'd say if you can fill out her team then she's still worth grabbing and investing in even without Rag Drag.