Well, the problem with that comparison is that Radiant Dawn didn't have good graphics for a Wii game. (although, most SRPG do look terrible)
From what I gather, it didn't seem like a big advancement from PoR. And since when is a 79 bad?!
That's a good score.
Gamerankings averages aren't very good indications of the actual quality of a game. Especially if the scores are of wide range. i.e. Lost Odyssey: Lowest:2.5/5, High Score: 96/100