A few thoughts:

1/ It's a mistake to get caught up in semantic distinctions and genreological quibbles unless there is something really important at stake -- and I wasn't at all clear what was at stake in your proposal of refolding postpunk into "punk" -- what would actually be gained except to make punk itself meaninglessly expansive? A historical sense of punk itself is best served -- and I think is actually more flattering to punk -- by the idea of it as a short sharp shock. That a lot of people got stuck on that particular moment (Oi! etc) is not necessarily to the detraction of punk itself!

2/ Swimming against the tide of "post-punk" as a discursive fact is futile at this point-- this term is in use (and was in use from about 1979 onwards, in the UK music press; it was well established long before I wrote Rip it up ) and therefore it has meaning.

It covers

 A/ the music that would never have been made without punk but that didn't sound like clash/pistols/ramones 

B/ the music that never would have found an audience without punk/independent label culture  (ie. pere ubu, devo, suicide, throbbing gristle etc groups who had been going long before pistols/ramones) even though it wasn't that punk rocky and was sometimes more extreme, antimusical, noisy etc than punk itself had been.

The post in postpunk refers above all to idea of the next stage from punk; it is not necessarily the refutation or cancelling or reversing of punk, but an attempt to move on from it, meaning not leaving it behind but using that (sex pistols or whatever) as the point of departure, the launching pad. 

But because people disagreed with what "the next stage" would be, and indeed disagreed about what the really important element of punk was, you got a panoply of directions, an ever-widening delta…

You might say that postpunk is the actualization of the internal contradictions of punk, or of the dissensus that for a year or so was actually contained within the consensus of the word "punk"

Eventually that actualization of contradictions/differences leads to entropy but the prime phase of it -- 78 to 82 is rich enough to be considered both a period and, if not a genre, then a space of possibility in which genres formed

The "post" in postpunk is similar to the post in postmodernism  -- the latter isn't the cancelling of modernism, but a kind of relaxing off its strictures, a kind of selective betrayal of its tenets, an attempt to move to the next stage or sidestep certain blocked paths and dead ends.  

The original impetus of modernism subsists in the very demand to keep on innovating; postmodernism was not about a simple return to tradition or classicism; it was a response to the becoming-tradition, becoming-canonical, becoming-institutionalised of modernism after WW2.   

A similar kind of complex set of reactions and relationships with the precursor informs postpunk activity; there is a simultaneous move of  keeping faith and breaking faith. 

From this point of view staying true to punk as a form  (Oi!) or indeed in terms of a narrow idea of its content (anarcho-Crass) would be to betray its  spirit (change).