Even if we assume they are significant groups, why couldn't a 1, for example, have an 8 wing (since they're both gut types) or a 6 wing (since they're both superego types)? How do we know the types are correctly placed? For example, 1s tend to identify with their minds, are often intellectual (especially 1w9s) and Sp 1s, (according to Naranjo, I think) are often more anxious than 6s, so there's a case for putting 1s with the head types; even Riso and Hudson say 1s tend to think of themselves that way. Meanwhile, 7s are a much more physical type who, like 8s, enjoy the pleasures of the senses. Many of them like their activities to be intellectually stimulating, but I don't think that's a core part of the type. They tend not to be very anxious (they fear being trapped and in pain, but all the types have a basic fear) so that's not a good reason for classifying 7 as a fear type. As for the Freudian groups, Naranjo talks about the "high super-ego" of 5s, and he portrays 2s as an id-ish/hedonistic type whose giving is about being seductive, rather than out of a sense of duty, or to earn love, as you'd expect from a superego type (and from the way sources like Riso and Hudson describe them).
As for the dis/integration points, if you divide 1 by 7 (7 being, of course, 1's integration point) you get 0.142857, and as you've probably noticed, that's the sequence of disintegration points. So I think it's another case of it being an elegant theory that doesn't necessarily apply all that well to real human psychology. A few of the dis/integration points make sense, but mostly I don't think it adds much to the theory. I believe the thinking among some people is that the patterns in the Enneagram symbol apply to human personality because they apply to any system or process and capture the inherent order within the universe. I'm sceptical of that.
I've had trouble settling on one type, and I've started to think that's mostly because of the discrepancies in the ways that different authors describe the types. There are several that accurately describe something about my psychology, but all of them have some key trait that I don't relate to (a trait that, according to some people, if you don't relate to it, you're not that type). I've mostly been flipping between 1 and 6. 1 because I relate to the perfectionism/criticality, inner critic, the sense that things are never as they should be, inability to accept my own mistakes, strong convictions, ETC, and I really relate to what Palmer says about how 1s pay attention. What I don't relate to is reaction formation. I can't think of a single example of a time when I've done that. And yet, the entire type 1 personality is a reaction formation against anger. Also, I don't relate to those SJ-ish descriptions saying that 1s are obsessed with neatness, manners, social conventions, ETC. Although some sources say that whether any particular 1 even cares about those things depends on their own individual standards.
For type 6, I've found that some profiles of the type describe me really well, and others are totally off. I'm not just talking about having a couple of traits that I don't entirely relate to, I mean that they're pretty much the opposite of what I'm like, what I value, ETC. Typewatch's 6w5 description is one of the best descriptions of myself I've come across, but most of what Riso and Hudson say about 6s is not me at all. Maybe that is to be expected, because of the phobic/CP distinction, but I don't really relate to either side of that dichotomy. I am far too cautious to be CP, and I don't relate at all to the idea of doing things that scare me to prove I'm not afraid or throwing myself into action when I'm anxious, but I also don't relate at all to the phobic descriptions about "warmth" and submitting to/wanting to be protected by some authority. On the other hand, the anxiety, worst case scenario thinking/contingency planning, not easily trusting and wanting open and clear agreements, dislike of uncertainty/ambiguity/unpredictability, even the "yeah, but..." way of thinking, I relate to completely. My way of thinking, and many of the assumptions I make about the world, seem very 6, but I don't relate to the 6's authority issues.
At one point I typed myself as a 5, and I can't entirely remember why I decided I couldn't be that type. It might have been because I relate to the compliant/superego group (when the descriptions aren't too SJ-ish, anyway). I relate to the withdrawn triad too, but lots of introverts mistakenly think they're withdrawn types, so they say. It might have been because I thought I wasn't detached enough (I've read quite a few forum/blog posts from people who are knowledgeable about the Enneagram, talking about someone who thought they were a 5 because they were introverted, intellectual and emotionally detached, but still weren't detached in the same way 5s are). Also, I don't think I have the pattern over my life that 5s tend to have, of avoiding obligations. However, I do relate to the search for knowledge, the strong need for privacy, the hoarding tendencies (I think; I don't collect things, but I do tend to hold on to things I haven't used for a while because of a vague sense I might need them someday), even the 5s attraction to/fascination with what disturbs them. I think there's a bit of 4 in me too, but I'm quite sure that's not my core. So I still take an interest in the Enneagram because I think it's got some insights the MBTI has missed, but there are a lot of intelligent, self-aware people who can't figure out their type, and that makes me think we probably don't all fit neatly into one type. Tritype isn't an entirely convincing solution because of what I said about head/heart/gut not being particularly significant groups.