What really threw me was your claim that a person eating pie has no way to know how delicious it is. Am I supposed to try to argue that eating tasty food is a good way to know what delicious is?
This doesn't need to be so complicated. I'm quite simply pointing out that if each and every pie you consume tastes exactly the same, there is no way to claim it's better or worse than any other pie. The same holds true for ideas like "good" and "evil". If one doesn't exist, then you cannot claim a polar opposite in the first place.
For example, the flat earthers will openly admit that there is a north pole, yet completely ignore the fact that you cannot have a north pole without a south pole. Polarity requires TWO poles. See the problem yet?
Likewise, you cannot logically or conceptually or meaningfully speak of "good" absent the idea of "evil". I'm not suggesting that good isn't good. I'm pointing out that it is not a meaningfull word without the idea of "evil". It is essentially equivalent to the idea of "same" or "sameness"
So while I can see that Satan doesn't need to exist for God to exist, it makes no sense to say that God is good when evil doesn't exist because without evil or the idea of evil, good is all there is. Again, it's like saying that nothing is good or evil. Nothing is the same regardless of how one describes it or whatever one chooses to attribute to nothing.
One must diligently distinguish between the concept of nothing (which conceptually speaking is something) and nothing (which doesn't exist) to comprehend what I'm referring to. There are no gradations of that which is the same. Nothing is a prime example, and when we apply this principle to your example of good without evil, we get the same result.
You claim that there are gradations of good, but this is just semantics because to diverge from either absolute or transcendent good, one is no longer on the good path. It's not a lesser or different path. It's pure evil. This is why Jesus says, "Only God is good".
The apple pies are good, but if they all taste the same, there is nothing to distinguish between better, worse, or pure evil. Good ceases to mean much of anything especially if they have ALWAYS tasted the same.
We don't live in a world where pies have always tasted the same. We don't live in a world where evil doesn't exist. You're pretending that we can understand good when it is the exact same as everything else. That's just a pipe dream. It could just as likely be pure evil. How would you know without anything to distinguish it from?