I found their prose to be quite good. It's sad that it seems long-winded to modern readers. These letters are not long. Maybe attention spans are too short.
Some of the "verbosity" seems to arise from their apparently mutual concern to preserve their relationship by delivering criticism of ideas or behaviors without attacking the person. We could certainly use more of this style of communication today, but all it earns now is a "TL;DR" at the beginning or the end.
It's amazing isn't it, the language that surrounds the detailed arguments. The constant attention to recognize the effort put into the designs and ideas, trying not to offend, but clearly still managing to do so.
My technical correspondence is nowhere near this kind, and I know that it offends in some cases, but I also find that anything over 2-3 paragraphs these days is generally ignored.
Email, texts, slack, etc. have greatly abbreviated our conversations, allowing for many more, but reducing their quality.
Some of the "verbosity" seems to arise from their apparently mutual concern to preserve their relationship by delivering criticism of ideas or behaviors without attacking the person. We could certainly use more of this style of communication today, but all it earns now is a "TL;DR" at the beginning or the end.