Alas! I completely forgot about this thread! Sorry I built up that answer and then bailed out!!
Fortuitous that you mention Aquinas! His "Best of all possible worlds" gambit is exactly the kind of hypothetical I was talking about. True or not, it shows that omnipotent goodness and the existence of sin are not an explicit contradiction."The theologian considers sin mainly as an offence against God; the moral philosopher as contrary to reasonableness."
Thomas Aquinas
While I think the import of Isa. 55:8-9 is huge almost never given fair consideration, I think this may overstate it. His ways and thoughts are higher, and that may call into question all human conjecture and allegory, but fortunately that is not all we have. It does not, for instance, call into question what He explicitly says about Himself.A well thought out response. Thanks.
I'll expand on your reference to Isaiah 55:8-9 by making the observation that its import would then first call into question the validity of everything we think we know about God and faith and scripture.