Basically, indeed. And that's coming from his biggest fan on CricketWeb.
I'd argue that his "****edness" was due mostly in part to the strange way he was treated by the selectors for the majority of his career though. He was dropped seven times throughout his Test career (IIRC) and it was only really justified twice - the first time and the last time. He was often dropped in that middle period due to ridiculous scheduling more than anything else - he'd get picked in the Test team, do enough to hold his place without being brilliant and then go into a one day series, play poorly (and he's always, always been a poor one day player; he doesn't even have a good domestic record in this format).and get dropped from
both forms due to the huge gaps between Tests New Zealand actually played. He was also dropped once for merely saying he'd prefer not to open - not that he
wouldn't open or resented the selectors for having to open, but that it simply wasn't his preferred position.
He's always been a bit temperamentally funny but he's scored a lot of pressure runs on difficult pitches in domestic cricket - what he needed was to be assured in that he'd be given an
extended run and it become obvious fairly early that this was never going happen. He was a complete shadow of himself in his last series against England - he just really didn't know what he was doing. He isn't the most mentally strong character of all time but I don't think he was, at least in the beginning, as mentally weak and nervous as is generally accepted. At the end he certainly was but there are reasons for this as I explained.
Now, he
did have a technical issue as well - his off-stump judgment in defense. However he's certainly not the only batsman to have this issue and I personally don't think his technique actually prevented him from being successful in Tests, particularly if you balance it out with his awesome powers of concentration and, when actually assured of himself, excellent shot selection.
He was always going to be an inconsistent kind of player but he's the classic example of selectorial mismanagement for mine.