Personally, I prefer the method that is currently used. What you are forgetting is that the items the companions bring back are FREE items that do not destroy or alter the terrain in any way. That means that when your base area is mined out, or while exploring a new area and you run out of materials to make extra bullets, etc. you can send your companions out to gather raw materials and be back in business without having to locate a new mining source. Similar to the Processing Station, all of these materials "appear" without the need for an actual resource in the vicinity, and they do it fairly proficiently. One thing I would like to see is to have the companions bring back rarer materials based on their skill level, with extremely rare resources found at the 3rd and 4th skill levels (like gold, diamond, titanium, etc).
I would also prefer using my own skills and upgraded tools to get the most I can out of my mines, instead of having a companion "destroy" a resource for a lesser gain. That is especially true if you have the skill tree active in adventure mode, and you have your mining skills maxed out. You can do much better than a companion mining rare resources like titanium and lithium, that currently cannot be accessed by the Processor or Companion, and so are limited (diminishing) resources in the game.
This may change at some point, but until then I prefer companions the way they are. I would interject that I would be in favor of them working using an easier "go work" access when you stop to build or mine, because having to tell each one from their individual screen is time consuming. Also try not to let them drop their bundle inside of other objects, especially if you are in a building or underground.