>Were the great dictators just irrational?

Probably not at all, although it's hard to think/talk in a general fashion about such large systems.

The Axis Powers strike me as fighting a more reasonable war than (for instance) their WWI aggressor predecessors if you view it as simply a grab for land and resources. It's a thing that a Khanate or a Roman governor would understand and appreciate. I'd say that the actions of the Germans and Japanese would make perfect sense to the ruling class of most pre-modern states.

It's hard work to avoid Historian's Fallacy.

If you want to summarize it in one sentence: yes, they were. In a nutshell, the argument is that the world wars were so destructive because the economic calculus changed, but people required the horrors of the wars to realize that the change had happened.

Not sure if this is sarcasm, but yes, I don't think you need to look too deep to see that.