Thanos slaughters Darksied if he has the Infinity Gauntlet otherwise he takes it 6/10 times. Thanos isn't just incredibly intelligent he is incredible strong keep in mind once he got the Infinity Gauntlet he literally killed every Marvel Hero with it. (In part 1 of infinity wars)
Thanos has a Infinity Guntlet to defeat Darkseid!!!
thanos is simply better than darkseid.