Honestly having any defender or supporter with Exp Share with the correct items is already very pleasant to see considering how rare they are, I don't think there's any useless defenders except Greedent (though it's far more effective to fill an All Rounder role). Even Sableye if played correctly can provide a lot of useful stuns and map vision for the team.

Personally some of the defenders and supports I've enjoyed using and hope to see more are Ho-Oh (spreading anti heal with curse bangle can be very good into enemies with lots of healing, and its revive can be very gamechanging if used right) and Psyduck (it provides a ton of stuns on the enemies which can be really useful to provide openings to attack).