These operations can be summarized by generalizations to be just insertions and deletions.
Most text editors provide text insertion capabilities by allowing the user to just type.
Text deletions are then accomplished by the use of certain non-typing keystrokes which are not allowed to insert text into the document being edited. VI is not one of these types of editors. Like anything different, it can take some time to get used to this type of editing. There are some real benefits to be gained from it. Some are quite significant, an others while perhaps not terribly important, are deeply rooted in the progression of computers and terminals.