Most of the ARX earned from mining comes from buying the limpets and selling what's in your hold at the end so I agree there is definitely room for improvement here.
If your objective is just to make lots of credits in relative safety while also earning significant ARX exobiology is the way to go. Sell your bio data one plant at a time for 22ARX each because selling a system at a time also earns 22ARX. The ARX earnings for exobio are not dependant on first discovery either.
I explore with my carrier in tow far from populated space. I gather lots of exobio data to sell on my carrier but every so often I need to mine tritium to fuel the carrier. I save bio data to sell if I want to top up my weekly ARX earnings to the 400/week cap.
I also earn up to an additional 400ARX each week in Legacy (the ARX all goes into the same pot so any PC player can potentially earn 800ARX per week), usually by bounty hunting in RESs in the bubble.
