You raise a number of very interesting issues here John, and as usual with a lot of conviction. I have taught about 'votes for women' for a number of years, and wrote my Masters dissertation about a small Suffrage group, the Jewish League for Women's Suffrage, and I teach almost exclusively about the Suffragettes. Why is this? I think partly it is because of what I was taught (not at school - even in the 1980's women were still 'hidden' from the school curriculum) at University - the course itself focused mainly on the WSPU.
I accept the points that you make about the splits in the WSPU, particularly over the continuation of militancy and the restricted franchise (which is ultimately what was granted in 1918), but it is interesting to note that despite the large opposition to the militants they were still able to hold fund raising meetings in June 1914 that raised the equivalent of a quarter of a million pounds. this would suggest that they were far from being a 'broken organisation'.
I would be interested to read your supporting evidence for this statement - I am sure that a historian of your standing would not be so mono-causal - what about the role of the First World War, or the resignation of Asquith?
As an aside, I recently gave an assembly for International Women's Day. One of the people that I had studied for my MA, Hugh Franklin, was a member of the Men's Political Union, affiliated to the WSPU, and the first prisoner to be released under the Cat and Mouse Act. I was 'pulled up' by one of the members of staff for a number of reasons - i) that I had chosen to talk about a man on international women's day ii) that I gloried in the 'violence' associated with the Suffragettes. I had to reflect carefully on the comments that were made, but I don't really have an answer to your final point.