Seems a pretty reasoned thread and I tend to agree.
1) I think this is the best possible definition of what constitutes a Head ON situation. I think most HO arguments are from people who disagree on definitions and they just end up arguing semantics (actually you can substitute just about any subject and most of them end up being semantic arguments because people don't accurately define what they're actually arguing but that's besides the point here

). If one plane has a solution and the other cannot get one before the merge then it's a front quarter shot. Otherwise you may as well say anything in front of the 3/9 line is a head on because it's impossible to say "a HO is anything in a 20% cone from the nose".
2) While I don't think the HO should be the first choice for anyone and is a tactic of desperation some people seem to not take this point into consideration. Why oh why would I want to HO if I'm in a P-51? A plane that in most situations can exit the fight and control the fight because of it's speed. The historical argument makes less sense to me because the stakes aren't even remotely similar, I think there are times when a HO makes sense, but I can't think of any case where it should be the first choice regardless of the plane I'm flying and what the other guy is in.
3) Situational considerations are where the decisions are made in my book, it's almost never my first choice but it may be what I feel to be my only choice depending on the situation. If I just had a knock down drag out fight with someone that left me low and slow I may take a HO shot if a A6M bounces my 38G, I may not still depending on my mood but I can certainly understand if the 38 would try one in this scenario. I'll also take the HO shot if I'm engaged with multiple people, to me the HO is no less dweeby than the 2nd, 3rd, 4th, 5th, guy who dives in once I'm already engaged.
I'll also add case #4 - sometimes I'm just lazy or in a foul mood.