I have been doing a lot of thinking about this thing and I think it DOES have a place... just not yet.
Now, you can take two guys out in a ship with 2 ROCs, scan, land, mine, repeat.
BUT!!! Some time in the future it is going to take TIME to get into and out of armor, and you will not be able to fly a ship in armor.
This means the 2 ROC method would lose a LOT of time with only 2 people.
With the DS, your pilot is your driver, and does not have to armor up at each landing, saving time. You have one less laser, but it is a better laser, more range, etc, meaning that overall it should be more efficient, once the armor changes are in place.
Nope, not it, hopefully.
Changing clothes and armor at your ships locker (once they come online in 2-5 years lul...) should take no more than 5-15 seconds. It is an inconvenience, yes, but nothing to cause hours of time wasted on a single trip...
If it takes longer, like we get a full animation of 3 minutes where our character puts on every single piece of clothing one by one... yeah, that's when they have gone too far with "immersion". They won't do this... (at least I really really hope they won't lol)
Also, the ROC / DS cockpit is as confined as a fighter's, so it would be pretty obvious that you should not be allowed to wear armor sitting in there either. Flight suit, sure, but bulky protective armor, nope. You should get into the ROC / DS pilot seat while still parked in the ship and not get out until you park it inside, cos no protective bulky armor. The other guy can wear whatever is neccesary and allowed in the miners seat.
This eliminates all the dress-up time.
Also also, if you have a ship with 2 ppl, you can be way more efficient just by having a pilot scouting deposits and picking you up and dropping you off at the right spot while you mine in a single ROC.
The problem is, this is all pointless debate as long as we cannot unload either the ROC or ROC DS into our ships properly! Which is as per last time I heard about it, the way they meant to work!
We will not be able to spawn storage boxes out of our pockets, so no using personal inventory anymore, and they won't be able to unload onto the ground or anything like that. So basically you will have to transport the whole vehicle to a station to sell off what's inside. This is very very dumb.
I don't know how they will solve this yet, but it's definitely not gonna fly. The obvious solution is open crates / dump trucks, heck maybe even a fuckin antigrav "wheelbarrow" or something, but without a way to clear the ROC's cargo hold into a container and keep on mining, they become basically useless.
No matter how much we try to figure it out, the sad truth is, the ROC DS was a fast and cheap way (90% reused assets) to add another cashgrab that is aimed at new players who have no fucking clue what mining in this game entails and they think "oh how cool, I can go mining with my buddy in this!". That's it. There is no higher purpose or future features or meaning behind it's existence.
So in conclusion This things only place is IN THE BIN!
The real solution by CIG should have been to Specialize them:
DS: Make it slightly bigger and slower. Eliminate the miners seat from the outside of the DS and add a larger enclosed cockpit for a pilot + a miner, control the arm from inside as suggested in the comments above.. Make the whole thing closed to withstand environmental hazards, including animals and whatever comes at you. Maybe add a turret on top with an FPS sized weapon, like a .50 cal on a tank, controlled by the driver so he has something to do while the miner does his job.
ROC: make it into an OPEN vehicle (edit: I've just been informed it already is. I never noticed lol), but one that would still not allow you to wear extreme-environment armor. So you would have to stick to moons and planets where a simple flight suit is enough protection. No turrets, cup holders or AC, no nothin. Just a mining lazor... Cheap and cheerful, very risky if you are totally solo in the wrong places, but could be employed in high numbers for efficiency as more of them fit inside cargo ships. Make it faaaaast, so instead of armor it can blitz about to protect itself.
This way, you get two unique vehicles with unique gameplay, and a justification for the higher price.. Simple ROC is cheap and small to carry around but only usable in "safe"-ish environs. ROC DS for env protection in very harsh conditions or where operating in large groups is problematic. Both would stand on their own, with unique capabilities to design missions for.
Then as they get the time, CiG could make more versions of both, like enclosed ROC but slower and much smaller cargo space, DS with larger hold and no protective gun, and whatever. It could be separate vehicles for them to sell, or just upgrade modules, or even in-game upgrade stuff if they wanna be kind to us players.
Instead they took the cheap and scummy route of a cashgrab, so no, I'll never accept why the ROC DS had to be this way...