Fail. If someone you call a "spammer" kills you, 9 times out of 10, they just spammed you because you couldnt stop them. Most "spammers" can block, and do, but its easier to keep turtles under their shields and just beat them into the ground. Same with tincans and the like, just keep hitting them, most of them have gimped builds that they have footshot by wearing silly amounts of armour, and have skimped on agility just to be able to get into their plate quickly, therefor lack wpf even more, but they 1hit, so you have to keep hitting them while you can.
So: Reduce combat speed is going to lead to same thing: Faster players will STILL be faster, will still attack nonstop when they know you cannot stop them, throwers will still be OP, and the game will be more boring. Just mho.