The premise of the argument that Venat wasn't faced with tempering and didn't do anything is visually represented in Game and disproves the argument. We see in the infamous "walk" sequence a roundabout portrayal of the situation where the Ascians were unwilling to focus on anything other than summoning. As far as tempering, you can't say "she had access to the futurre information" only when it's convenient for your trolling. If she knew tempering was going to occur at any time, obviously her response would be based on that. Her reasons for sundering are boiled down to stopping Zodiark but obviously that isn't just a personal grudge-- it's because of how he affects people and what he represents. That's what you're glossing over to make some weird argument about EW.