I don’t know enough about the arbhar to give a fully educated insight into this comparison, but I think it’s likely that arbhar will be more specialized and do granular in its own way better than if you were going to try to recreate it with the 301. That’s not to say that the 301 granular isn’t amazing. The flip side is arbhar won’t be able to do granular like the 301 (buffer time, buffer editing, real time granular, having access to way more material via the sd card, etc), as well as everything else you can do with the 301 which is literally overwhelming. Also, arbhar seems to have an amazing reverb which really enhances whatever granular stuff it spits out.
I think you could confidently replace clouds with the 301 save for reverb. In my opinion reverb is the big hole in the 301. The available reverb is barely fine. I use other stuff for reverb, but it would be cool to have something better in the 301. The delay options are amazing though. But, even with all the delay options I still have a magneto and mimeophon in my case.
So, long story short: if you like granular I’d get arbhar and 301.