I will tell you what our experiences were on our last trip during Easter week. We made some ADR's, which we kept and it worked out well. There were a few times that we had planned on CS, but were in the mood for TS. As long as we were flexible, we had no problem finding a place to eat. You can go to any restaurant or guest service location to book for any restaurant on property.
One day we were at MGM and at about 5:30 we wanted a TS dinner. We walked over to Sci-Fi to see if we could get in for our family of 6. They didn't have anything, but Brown Derby did. As we were walking away the other hostess, who had been on the phone, said she just had a cancelation and they could seat us right away. I know that this was very lucky, but on another day we did the same thing at Epcot and had our choice of restaurants in the park.
As long as you are flexible, I think you will be just fine getting ADR's when you get there. Have a great trip!