People misunderstand what those limitations mean.
Lucifer can't create something out of nothing, i.e, ignore conservation of energy. If he uses his own energies he can perfectly do them.
Michael is simply not a very good Reality Warper, though as shown when Elaine got her father's powers, he is very much capable of doing Reality Warping and stuff of the like. He can Reality Warp things, he just can't Reality Warp on the infinite scale of his power.
This is meant to illustrate the complementary differences between the brothers. It's a narrative thing, more so than a power-level thing.
Michael is the Embodiment of God's Infinite Power, and thus his light can create anything and also destroy anything. Lucifer is the Embodiment of God's Infinite Will, and thus he can shape everything and do anything, as long as he has the energies to do so. One has Infinite Power but finite applications on such a scale, the other has finite power but infinite applications to his power. When together, the two complement each-other.
Also, both Sandman and Lucifer are deliberatedly vague about the level of power of its characters, and avoid fight scenes at all costs. This is why it's said that Lucifer and Michael created "A Creation", and not a universe, multiverse, omniverse, or any other word you can think of. They created the totality of existence. The scale of that totality is not important.
