If they don't change moves, they should keep performing the same as the did before.
However, with the new system some defenders will probably be more relevant, so some movesets might become more valuable. So lets say if a lot of psychic types become popular gym defenders. (Slowbro/-king, Espeon, Hypno...) B/C might become better/more valuable than B/SE on Tyranitar.
But we will have to wait and see.