I'm going to go out on a limb and state my opinion that Block (makes more sense flavor-wise than SW) + Encore is not broken. We are not talking about Wobb here, people!
Consider this scenario: DLL against whatever. Now, either the opponent will switch out, or they will not. For the sake of argument, we'll assume they switch. If they don't, then either 1) they have a reason for it, such as attacking you or setting up, and as such don't want to switch, or 2) they deserve to be set up on for not utilizing one of the most basic tools in the trainer's arsenal. Assuming they switch and you Block, now what? Your opponent is not going to switch to a pokemon that cannot do anything to the DLL, so we'll assume that the opponent is going to do something like use a high-power/STAB/SE move that you really don't want to be Encoring. It's also probable that they would bring in a Taunter, which would completely screw this thing over (can't use Encore after Taunt). High speed + Encore can also be a curse at times, as you can't Encore something slower that just switched in; this further hampers the Block + Encore strategy. In addition, Block takes up a precious moveslot, limiting your options to something like Block/Encore/set-up move/attack. Potent enough if you know what you're doing with it, but not a direct threat to much.
The only argument I see for Block + Encore being broken is that the Encored pokemon is forced to repeat their move again, instead of switching out (as with "normal" Encoring). But let's be realistic, even a set-up Bellyzard isn't invincible. There's no way you can argue that giving something 1 free turn is gamebreaking.
Not that I'm saying this would be useless, but it's nowhere near the level of brokenness that's being claimed (without any backup reasons, I might add).
