Forgive me, but I remain mystified as to how one could possibly define any kind of absolute as opposed to subjective morality contra God in the event of God's existence. Again, if God has the position with regards to the universe that He's constructed as having in Western thought. If it's otherwise I don't honestly understand why we would even be talking about this.
I don't really understand how this argument is different than "that's just part of God and we know it is"?Because
if God has the
rest of the traits defined in Western theology, then I don't understand how there's any basis for holding back on omnibenevolence. It's conditional on the idea that that's the concept of God that we're going with. If you want to discuss concepts of deity more generally in this area, then by all means, I'm fine with having that conversation too.
We are judging God using a standard related to our observation of existence when we use analogies like perception and thought process to describe things that He does or that He might do. Thinking of God analogically like this demands, technically, a position of agnosticism, yes. It doesn't necessarily demand
de facto agnosticism, since we can still determine which of various possibilities of God's very general nature we're talking about and go from there by analogy. For example, if we were discussing the set of possibilities relating to how the universe would work if the supreme existences were the kami, then we'd have an opening to discuss concepts like humans being destined prey of the gods or the gods existing in a dangerous symbiosis with humanity and nature. Since we seem to be discussing the set of possibilities relating to how the universe would work if the supreme existence roughly resembled the God of the Book religions, we have an opening to discuss concepts like omnibenevolence and how it relates to the fact of having created the universe and everything in it (including such things as 'right' and 'wrong'), even if we don't (as I assume you don't; you may correct me if I'm wrong and you're doing something Socratic or diabolically advocative) actually think that this is the way the universe does work.
As for how one can be other than agnostic while taking the position that thinking about God in terms of what is observable will be analogical at best, there are at least two ways to go about this. We can make an attempt to assign probabilities or guesstimates as to the likelihood of different conceptions being the way things are, and/or we can do it emotively or volitionally (the 'leap to faith'). In fact if you take this position
any belief or strong hunch about God, even strong agnosticism, is one of these things.