Yes, for multiple reasons. The first reason is that Sigil is unfortunatly no longer actively maintained/supported. There is a big problem finding enough programmers with knowledge and free time to work on it. So, untill there are additional programmers, development is non-existent.
The other is that BookView is not a good way to enter texts for an ePUB. It can be better done in CodeView, but basic HTML knowledge is required. Copy/pasting in BookView is bound to give issues sooner or later with formatting, as the Sigil must make several guesses.
In spiritual successor of Sigil, the standalone editor function of Calibre, I believe that that only codeview is available for editing.
Have you looked at Yutoh? I don't use it myself, but I think it might be more what you want.
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