No, that's just plain wrong. Arsenic is what allows NovaGrabby to beat a CC stall like Monoentropy, or even a Firestall that doesn't draw what it needs (save Shriekers and Lightnings for OTK), and it's not slow at all. It's the fastest weapon we can use in a rainbow, and the fastest standalone weapon too.
Forest Spirit adds CC-resistance to complement the weak Shriekers, and has also been crucial in some matchups during War 3. It's more offense, and it's reliable. There's no reason not to have it in a rush.
We used Fog a couple times, but it's pretty useless in NovaGrabbys in War because our NovaGrabby crushes rushes with Lightning anyway, and most rushes pack PC.
Our NovaGrabby is one of those decks that have evolved over a long time. It's customisable, but the best versions have shown themselves through actual matchups in War. It has achieved an optimal design and can't be improved, only changed to fit a certain purpose.