Hi Chiicken!
Your reasoning as to why answer choices (A), (B), (D), and (E) are incorrect is spot on--great job at eliminating those losers!
So let's talk a bit about your issues with answer choice (C). First, you note that the main reason you chose this answer choice is because the other answer choices suck. That's a perfectly valid reason to choose an answer choice! Remember that our goal is always to choose the best answer of the 5 choices provided. That sometimes means that the correct answer will end up being an answer choice that we don't really like, but it's still better than all the other options we have. This is why eliminating incorrect answer choices is just as important a skill as recognizing a correct answer choice. And it served you well on this question--you figured out the correct answer because you recognized why all of the other answer choices had to be incorrect! Great job!
But I know it always feels better to really understand why a correct answer choice is correct, so let's talk through your reasoning a bit about this answer choice. I agree that the LSAT is conducive to overthinking. Unfortunately, I can't give you a precise line to tell you when you're thinking an appropriate amount vs. when you're overthinking. You get a bit of a natural feel for that the more LSAT questions you do, but sometimes you need to rely on other skills to help you out (like eliminating incorrect answers!).
With this answer choice specifically, it does tell us that the renewable substitutes would be "functionally equivalent," which basically tells us that they would function in the same way, thus allowing us to accomplish the same things. With your example, if we run out of bronze, we won't be able to make bronze swords or bronze shields, but we'd still be able to make swords and shields. I think your example with bronze might have caused you to focus more on specific products rather than on a broader idea of accomplishments. Try thinking about it in terms of energy sources. If we run out of coal, we won't be able to power our electricity using coal anymore. But we'll still be able to create electricity using other resources, like wind power. So we can't accomplish "coal powered electricity" anymore, but we can accomplish electricity. So the idea is that you can do the same thing, just using another material. We can still create swords and shields without bronze. In this case, narrowing our definition of accomplishments to be based on the material used (e.g., "bronze shields," "coal powered electricity"), is going past that "overthinking line"
Hope this helps!
Best,
Kelsey