I think you should continue if he's still enjoying himself and isn't losing confidence by bumping into things. It sounds like your trainer and the other handlers are doing everything possible to help Dylan, and it may be helping Dylan to adjust to the changes in his sight if he's working in a safe and controlled environment.
My very old Cocker gradually went blind in both eyes with age related cataracts. I continued to let him off lead on his walks in the New Forest for a very long time, but selected the safest places I could (level ground, no brambles, trees, ditches etc.) and it helped to keep him happy and confident.
Good luck with Dylan. Dogs adapt amazingly well and he's probably less worried about it than you are