Yeah, depression does that, so I honestly wouldn't be hard on yourself.
When I was going through hard times at uni, I remember feeling that way. Ironically, after my second year (4 year degree in Scotland) I really had no idea where I was going with my degree. So, I took a year out, worked in London within industry, got a fresh perspective in life. The university bubble does that, because employment is different to academia.
As I am sure you have also found; the problem lies with motivating yourself to study, as opposed to actually studying. Which when it comes down to it, from my experience, it was all exam techniques and working in groups. Sharing knowledge with one another. I think you labelled this as rote learning earlier. A 2.1 student doesn't as you rightly put have to be a genius, he just needs to know how to grasp concepts and work hard. The difference in intelligence is the time taken to grasp concepts, with one guy it may take slightly longer then the other, but as long as they grasp the concepts, who cares?
This is why university is not a good indicator of intelligence, because there are so many other variables in play which can cause a fail to under-perform. If you take into account personal issues that may happen, you cannot base someones business acumen on how consistent they were. Due to it not being an even playing field from the outset.
Physics Enemy, you sound like a really smart guy, that is clued up about ****. I would employ you, because you have good interpersonal skills, which is probably much more important then the degree mark. Given, you are working in a team in most organisations. Many 1st class students I knew, were socially inept as hell.