Right, like my edit of the post you quoted noted: mass of the brain relative to body size is whats most important. An elephant has a larger brain than humans, but its such a smaller percentage of their overall body than humans that they aren't smarter or even nearly as smart. Its weird how it all works. Anyway, Neanderthals were shorter than homo sapiens, but also stronger, so overall body mass might be a wash comparatively, which as far as my understand goes means that if Neanderthals had survived, I believe they would have grown to be a smarter species than humans.
Absolute breeze. If you put a human brain inside a dinosaur it would still be a human brain. If you took it out and put it in a jar so it now makes 100% of its total biomass then that doesn't mean it becomes hyperintelligent. Body size has nothing to do with intelligence whatsoever, it's the ratio between the prefrontal cortex and the brain size.
NB: That's not to say that there isn't correlation between brain size and body size, but that's correlation, not causation.