He didn't go around beating people up in Thanos Quest. I don't think he actually engaged in physical combat with anyone but Champion. It was mainly trickery and manipulation. My favourite was what he did to the Runner. Also the part with the Gardner was fantastic where Thanos genuinely begrudged what he had to do. Showed that he isn't just some cackling, one dimensional villain.
I wouldn't say Darkseid is more complex than Thanos really. Darkseid is a concept, there is no room for development or him changing. He is what he is. Thanos isn't. Doesn't mean Darkseid is less compelling. But yea, i wouldn't call him complex at all.
I think with Darkseid and Thanos you can basically sum up the differences between DC and Marvel. DC is more about their characters being Gods, concepts, myths. Whereas Marvel makes them more human and relatable, even nihilistic, nomadic demi Gods like Thanos.
And glad we can agree about Giffen, he's awesome. What the hell is he doing these days anyway?