Greetings!
Yes... during my resolution tests, I found the 10x25 compacts to have better resolution across the FOV than full-size x42 and x50 binoculars. Counterintuitive, I know, but I can't argue with the results. They were also sharper from edge-to-edge than the full-size... in fact the 10x25's have THE sharpest edge performance I've ever seen in ANY binoculars. I don't have a reasonable explanation, other than perhaps less light-path curvature due to the smaller lenses? Just guessing.
As for the consumer guide testers rating the Nikon 10x25 better optically than the Leica, I have no idea. Perhaps user bias or sample variations? I know that when I went to buy a pair of Leica 10x25 Ultravids, I brought my Nikon HG 10x25's along and there was absolutely ZERO difference in ANY test I could devise - and I did take my resolution test chart along. I was so impressed that two different binoculars were so optically similar, that I even briefly entertained the idea that maybe the designs had been stolen!
I found contrast to be identical between the two as well... in answer to your final question.
I would strongly suggest that you find some way to compare the two side-by-side yourself, especially if you are considering a purchase sometime in the near future.
Best wishes,
Bawko