Those are very good points. Both this particular song and the album as a whole is quite varied, and both in a organic way that feels natural and your observations about how a lot of people write and talk about the albums as 'proggy', 'straight rocking' and so on are also spot on. Why does those initial labels stick?
The press release at Rune Grammofon may indicate an answer: 'The initial idea was to collect big riffs on one album and do a pure hard rock record' it says, and 'the main musical thrust is pretty full-on, even by Motorpsycho standards'. I guess it is easy to get coloured by that, you have an entry point to a new album, and I suppose a lot of reviewers also go to the album with that in the back of their mind, not because the are lazy or bad but just because that's how the mind works. And then the those characteriations get repeated and take on a life on their own. (Heck, I know people who still are under the impression that MP is that alternative, heavy, noisy outfit it was 1991-1993!)
As per usual with an MP album it turns out to not to be quite that easy (as in fairness Rune's press release also says), they are usually more multifaceted than that, and yet having that unmistakable and everpresent Motorpsychoness that shines through in their songwriting, arrangements and playing, and those (like most of us in this forum) who listen will discover that, and rediscover and reappreciate albums again.
Watching this guy discovering MP was quite nice though. That grin on his face!