As for nerfing arc, my position on that shifted over time:
When it came out I was excited for it, and would've been disappointed by a nerf because I didn't see everything coming, just that it was *really* good.
When I started to see its full potential, I was in favor of a nerf. There would've been a few people that would've gotten a large advantage, but the majority would still be on a relatively fair playing field.
When years passed and "everyone" had one, I started to feel it was impossible to nerf, because it'd create an unfair wall for those who hadn't already taken advantage. There would always be literally hundreds of people on each world with these super-buildings, and the path to get there for a new player wouldn't really be there.
Now I think they could nerf it again, because it wouldn't have near the impact it once would have at slowing people down... There's so much raw FP production now that people could power through without an arc. It might add like 30-40k FP cost per building to get it through the "was-sweet-spot" - but that's only like a month from once your city is well-developed with event buildings - and even less if you insert yourself into a GBG farmers guild. And that's if the bonus was eliminated entirely. If it got lowered to like 1.5 instead of 1.9 at 80, the loss would be even more manageable. But given that reasoning, I also don't really see the point of nerfing it anymore. It wouldn't return the strategy to the game.