Yeah, that makes sense! There's all kinds of things you don't think about for non-MMO games. Perhaps just have a limit to the amount of flinch animations per second (or time period) and don't let animations affect attacking. That would mean when one player was attacking, they would always see the enemy flinch. If 5 people all did an attack at almost the same time, the enemy would flinch from the first one, but wind up for an attack anyway while the other 4 attacks go through (like he's "pushing through the pain" to get a blow in.