Not using real characters, and using baseline adjustments and font size tweaks, also leads to an endless stream of duplicate threads like this one.
Even for text engines where the above isn’t a problem and it overrides the literal definition of a line-height multiplier for those special cases, I still classify the whole word processor baseline approach somewhere in the same neighbourhood as Word’s “bold” and “italic” buttons, which always work, even if the font does not have those variants. In that case it does so by adding more pixels around them, or crudely skewing the letters, respectively. It’s a brute force approach that’s maybe acceptable for office memos and personal letters, but ideally has no business anywhere near a book, paper or otherwise professional document.