I built a fusion reactor fine just using quarries. I know thy're not everyone's favourite form of mass resource gathering but your post makes it sound like endgame is unreachable using quarries, they're fine.
I definitely agree. End game is PERFECTLY reachable using quarries. It is also reachable with iron picks, it just takes a lot longer.
It's all about how much time it takes to gather those resources. If I can mine more ore with 2 turtles, at a fraction of the start up and energy costs, how much more "reachable" does this make end game? Again, any solution works... eventually. It's more a matter of how easy it is to get there.
My statement stands in that by the time you are looking at a Fusion plant, you should have access to much faster mining solutions than the quarry. This doesn't mean you can't get there with quarries (or iron picks), and if my post inadvertently implied this I apologize most humbly.
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A reasonable facsimile of intelligence...