Right. My own perspective into this might carry some comparison as Norway are also not part of the EU, as I am sure you know.
There are multiple agreements of course, which bind Norway to the EU in multiple ways, displacing power out of the country.
 
Personally, I agree with you on the principle of democracy and voting connected to what goes on where you live. This is one thing that I also don't like about the EU.
Today's society is much more intertwined though, and both through agreements with the EU and multinational companies operating, manifested through money, people, goods and information flows and more, power is quite widely distributed, privately, in bureaucracies etc. So, how decisions are made becomes quite muddled, and the world is so interconnected. But yes, in principle I agree. However, it begs the question - how much do the UK decide now, compared to before?  How much are they tied by their dependency on others, i.e. through trade? Is the UK stronger now?
 
As for the second part, I guess I am just as curious towards positives as I am towards challenges, if it is possible to say much this early, or as you say, what is down to Brexit and what is not? I am sure both good and bad things the different sides claimed would happen have, and others not.
 
When the debate about membership or not comes up in Norway, some of the key issues are control over our natural resources, particularly the fish, and principles like yours, displacing power and decision making further away from our own political institutions. The colonial past also plays a part, being under Denmark, then Sweden, for hundreds of years makes people not want another overlord. I also think the EU is more of a political, capitalist tool than this idealist "union" of one, and more of a trade block to compete with China and The US. So I am not too keen myself. I believe more localised, community based power is a good thing, closer to the people themselves. But that is another story.