Okay. Prove it. Prove that the Cataclysm is objectively, verifiably bad.
Because it killed a lot of innocent people, and the "good" gods took part in it. Therefore, the good gods committed an evil act, yet the setting still pretends that they are deserving of worship (it's a major plot point in the War of the Lance novels that the clerics of the good gods need to return).
And there's that fact that Dragonlance focuses on the "balance of good and evil", which is a bad trope. As you noted, Chaos and Law works for two cosmic extremes that need balance in a setting. Good and Evil don't need balance. Evil doesn't need to and should not exist. Evil is bad. Good is good. Yet, Paladine, the Top God of the Good Pantheon says that too much good is unhealthy and that good having too much power is bad.
In other words, "Good" in Dragonlance doesn't actually mean "Good". Because the people that the setting says are good people (the Good Gods, the Kingpriest, the White Robed Mages), aren't actually good people, because they tolerate the existence of evil and allow for terrible things to happen because they believe in the Stupid Neutral stance that Evil should/needs to exist.
"Good and Evil are both valid and need to exist" works as a meta-justification to create never-ending story hooks in the setting. Not as an in-world justification used by a Good God for why good is actually bad.