> MS Word is properly great if you only use the custom style rules (basically CSS classes) at the paragraph level, and never directly apply styling (basically inline styles) except for super basic stuff like making a word italic

MS word also has character styles (like a CSS style on a <span>). IMO you should use instead of bold or italic.

(There are three more types of styles: linked, table and List. See https://office-watch.com/2022/word-five-types-styles/)