with more and more cruise lines no longer allowing discounting of officially announced fares (I'm not talking about "brochure rates"), the position of specialized cruise agents has been improved.
If you know exactly what you want, you might want to go with one of the "big players", but if something goes wrong, you might be on your own. However, personally I would always prefer booking with a specialized local travel agent.
You indicate yourself that the number of offers is huge and almost confusing. Allow a professional TA to help you find the right cruise for you. I'm sure you will be happy to have gone that way.
BTW This comes from somebody who is not
a travel agent and who has no advantage whatsoever from expressing this opinion.