I seriosuly doubt that every calibre user will use the delete specific format function, rather like every calibre user not needing to adjust calibre's author sort algorithms
Instead, I worry about those calibre users who might be affected by this bug and in addition have copied some important files into their calibre library inadvertently at some point in the past. Adding a bulk check option will pretty much guarantee they will use it, and therefore end up deleting those files as well.