Second, what does そこに mean? I’m sure it’s saying “that’s why…” in the same fashion as そのために or そこで, but I can’t find anything on そこに anywhere.
I could be wrong here, but I think そこに here is being used as a way to add an additional comment. I know that そこに can be used somewhat like “additionally, moreover”, and in this case I could see it being something like “~~… and (moreover - to comment further on your ability to do what we can’t) it’s exciting/shocking” or something like that.
Or something else I was thinking, since そこ also means そのこと (source: デジタル大辞泉), I could see it just being translated as “in that (you can do what we can’t easily) I’m shocked” but I’m not too sure. I’m just kind of brainstorming ideas here. I personally would think it’d be the former (moreover/to comment further) meaning.
To your first question, see: nuances - が and に interchangeability and difference in meaning - Japanese Language Stack Exchange
tl;dr it’s like used like “not doable for/by/to us, …”, basically
That answers my first question, thank you!
