When will the writing of an email behave more like a word processor?

Currently (2023) , I find that when composing an email, it does not behave like a word processor as, I believe, it should.

For example when I paste text over existing text, it seems always to create a new line despite there being enough room for the paste.  And, after typing in larger text, pressing RETURN and then choosing smaller text for the next paragraph, this is ignored and the larger text is continued.