I'm currently on a holiday in Greece that we booked ourselves after talking to a travel agent. Her main contribution was suggesting an island to stay on, but all her other suggestions ended up being worse than the options we found for ourselves. For example, we wanted a quick cheap stay in Athens so we could see the sights, so she found us some hotels that were somewhat outside the city centre - I'm sure they were okay, but what we actually wanted (and ended up booking ourselves) was a holiday flat in the city centre with a perfect view of the Acropolis, the flexibility we needed to sort ourselves out for breakfast and lunch, and a much cheaper price point.

Likewise, we wanted to stay in a resort for a few days afterwards and relax, so she sent us some ideas, but they were so lacklustre that we almost gave up on the idea of that part of our holiday altogether. Then we found something ourselves that was much nicer, and have been enjoying lovely beaches and incredible food for the last few days.

Even her flights were weird choices that involved a lot of waiting around at airports and would have brought us back a day earlier - booking them ourselves got us cheaper and more convenient options.

I always assumed that a travel agent would be more convenient than looking for something yourself, but I was amazed at how poor our experience was using one. Less choice and flexibility, and as you say, less self-service, and for us self-service gave us exactly what we wanted.