However, this point is an irrefutable one:
You're right here. He did it alone because he didn't want any of his friends to die because of him. However the other list of authorities that you mention here, who he leaned on for support (outside of simply, survival) is definitely more authorities than an 8 would bother with.
Making an alliance with Dumbledore is intelligent: it's a matter of having power in the school. If you have the most powerful person in your back pocket you have more power. Bingo. Some people would say this is 3-like thinking, but I think if Corporate CEO is a stereotype for 8s, too, then 8s must also know how to climb up the ladder.
I'd agree, though, that Harry's particular method of suckuppery is a tad un-iddish, but it still *could* fall into the category of survival mechanisms, or gaining power, as a behavior (but you're right to point out, the motives are probably different). Living with the Weasleys could be seen as an act of seeking survival opportunities. However Lupin, Sirius, etc; unnecessary. Still, having allies does give a person more power. But the reasons are what we'd be looking at, in terms of enneagram. I can buy your argument that he did this because he is seeking a new 'family structure.' It does make more sense, with his character, than doing it because it's pragmatic. He gets very attached to these people and their place in his life. He goes to them for advice regularly.