For context, my wife and I are UK residents, who sail exclusively with Cunard, having enjoyed many cruises/crossings, all of which have been booked direct.
We have not encountered many issues over the years, but when we have, they have all been resolved direct with Cunard in a swift and efficient manner – no “tediousness”, no “hassles” and no need for anyone to “fight [our] corner” or act as an “extra level of travel insurance”.
Based on our personal experience of dealing with Cunard direct, I have not read anything in these posts which, for us, would warrant using a TA “to cover all bases” … but perhaps I am somebody who “won’t ‘see’ however many explanations are given”!