While I agree that the leg-sweep combo definitely needs to be adjusted, everything else about Valk seems okay to me. The biggest issue I face against them is when they do the shield-bash attack and knock you down, then do the left-right-legsweep as you're standing up, leading to an unavoidable second knockdown. One knockdown is fair game, sure. But chaining it into a second one that can't be avoided lets the Valk get in waaaay too much damage for a single knockdown attack.