The Canon TCs are quite sharp, but it's generally agreed that the Series II is not as good as the Series III.
I use my Series II a ton and it's incredibly sharp.
Here's a 100% crop from my 500mm/1.4x/7D combination (this is slightly reduced from pixel-level, but only a little to display it. Take your browser up to 200% and you will have overcompensated.):
Detail of broad-tailed hummingbird.
, on Flickr
BTW, I blew up your image to 400% and couldn't find the focus point. All those leaves and limbs with varying depths makes it hard to find focus. On my example, it's easy to find (on the eye). The DOF was deep enough to include the back feathers.