Any shielder who just holds down RMB while backpedaling and being too scared/bad to attack deserves any bug, exploit, or glitch possible to get them killed, its a terrible playstyle that should be nerfed to the ground.
Whenever I play shielder I have attack held down way more than block, and just tap blocks like any other melee class unless I'm shieldwalling or hiding from ranged. Never notice any downsides, "shield lag," or whatever like this, just that I can put all my effort into offensive positioning and let the RMB bubble handle my defense.