Sorry meme but we are going to agree to disagree on what it does being "right" on this one
I don't want my headings to have the same style as my paragraph text. *Ever*. But that is what the current Sigil behaviour does. In the "good old days" if I had a really badly formatted document (maybe a bad ocr where a regex isn't going to find all occurrences) I would use Book View to scroll through, fix paragraphs, chop pages, give the chapter headings an h3 or whatever style, flick to the stylesheet to add h3 {text-align: center} and it would be job done.
However now it is pointless using the book view style dropdown. Inheriting its existing styles is in my mind a regression that took place in 0.4.x compared to its original behaviour. Clearly you know way more than me about how difficult this is underneath the covers, I just found it strange it used to work the way I want it.