yeah, i remember a panel where his size dwarfed entire planets, he also destroyed all life in a galaxy, absorbing all the souls within it, and became much more powerful, to the point where he threatened death herself, she even hid in a mortal body from him.
yuga khan's feats are not that impressive, the only things he did, is drain some planets, destroy the apokolips armies, and cut the connection between the source and the other gods. The only way yuga could possibly defeat walker is if he had power over the souls (this is how death beat walker), in which case, yuga didn't display such power, thus walker wins without much trouble.