They aren't arbitrary, as I said earlier I got the LLM to de a detailed analysis first, then summarise. If I was doing this "properly" for something I was doing myself I'd go through the LLM summary point by point and challenge anything I didn't think was right and fix things in the skill where I thought it was correct.
You aren't going to have much success with LLMs if you don't understand that their primary goal is to produce plausible and coherent responses rather than ones that are necessarily correct (although they may be - hopefully).
And yes, Skills *do* make a significant difference to performance, in exactly the same way that well written prompts do - because that's all they really are. If you just throw something at a LLM and tell it "do something with this" it will, but it probably won't be what you want and it will probably be different each time you ask.