And they did have a plan based on a better understanding of at least some aspects of the situation: they understood the value of the Fremen, whom the Baron refused to acknowledge as important until Hawat opened his eyes. Aspects which didn't matter until much later if you count Paul's resurgence, and which resurgence involved some pretty exotic factors I can't really blame the Harkonnens for missing.

Well, they could have mattered, if the Atreides had more time to implement their plan. I'm not sure what point you're arguing against there - I'm not saying they had a better grasp of reality than the Harkonnens in all respects or even on average.

The Atreides were little morally better than the Harkonnens, Herbert tells us

That is a very strange idea; where does it come from? I'd have said the moral superiority of Atreides over Harkonnens is overwhelmingly obvious, including to in-universe third party characters (e.g. Count and Lady Fenring).