It just wasn't. You can still twitch. You just removes some of their DPS.
It is a better idea to stop twitch than removing glancing blows while moving.
By removing glancing blows while moving, you have penalized those of us that were moving but not trying to twitch.
I like this game because of the active combat. That is the bigest seller of this game to me. When I'm playing, I'm moving to flank and mitigate some damage so I'm not going crazy with the resource usage or if I'm in a group I'm not a drain on anyone that is playing healer.
About the only time I'm not moving is on a raid boss for the group gank. All other mobs I'm moving and flanking, not twitching.
Your idea, while removing some DPS from those that twitch, did not stop the actual pratice of twitch.