I think you are overly thinking what all a TA does or what control they have. I use a TA and I have 100% control over my trip. Some people like a TA's services and pay extra for them to do all the ground work. I do my own research and know exactly what I am getting into. I do my research and know what I want booked and they book it. If I have specific questions, as good agent will know the answer and or offer suggestions. I look online and play with the booking tools to check for price ranges and for specials. Once I decide what I want I have my TA book it.. for many reasons.. 1. I get the OBC
2. They look for price changes for me and adjust
3. If anything comes up, I want my agent to do the dirty work and beg Disney for exceptions. I figure an agency that brings millions to
DCL/Disney has a better chance of any exceptions.. ( cancelling or changing). I once had a change request that was technically not possible and my TA dealt with it and got it done..
4. Once I know what I want I can say what are the best cabins ( based on my must have and would like if price right) avail. for this price range... and they give me a list.. better than me searching different decks on the online tools.
The TA is only the middle man when it comes to actually making the booking and payments. Payments go directly to DCL/Disney. You are not paying the agent( unless you have one that does extra stuff and that is billed separately).
EVERYTHING else you control, whether it checking in online for your cruise and setting up activities or booking FPs or ADRS...
They always have your best interest in mind as they are only interested in what YOU tell them as the client.