Two questions, here. First, why do you think the graphics are poor? Second, why do you think Ghirahim and Demise are poor villains when they're not?
Ah the first is because they are poor, there is no denying that this is an SD game with jaggies all over the place and low res textures. You only need to look at these textures on a 40inch HD screen in the confined tunnels of the Lanayru facility to see they look washed out like a printed page that has had tea spilled on to it, there are ugly blotches of purple and it just does not look nice, like an internet picture that has been blown up to an inappropriate size. Another place where it is noticeable is after the sand pit has drained after the Molderach, just look up and see my meaning. Another example of where they were really bad is on the chained up area on the sand ship, those chains looked like they would look in place in the OOT era. The game would look much much better in HD which is why It I made a point of it.
As for your second query. I never said they were poor villains did I?