Psychic Whisper, I thought the thread title was a little confusing, too...and I thought you were contradicting yourself with your second post.
So if your looking at raw base stats, the most powerful non-legendary, NON-psuedo-legendary, Arcanine wins there. But as far as most powerful in general, well that's in the eye of the beholder. I personally think Bronzong, Lucario, and Milotic pwn souls, but they may not be the MOST powerful to someone else. I've seen some Underused Pokemon be absolutely deadly in the right hands. And Meganium's been a powerful part of my team.
Sorry if that was a bad response to this topic...