Actually, people explicitly didn't see Thatcher as "prime ministerial" when she first became leader - she had to work very hard to create the right image, changing her accent and mannerisms and style of dress, and working to master policy briefs that she was seen as very weak on in 1975 (especially foreign policy - her first foreign policy trip to the US was a disaster).
Well exactly. It was a hurdle that she overcame before election night, that Red is slowly apparently getting over but not one that Kinnock got over (it didn't really matter if this was an issue for Ashdown, he had bigger problems).