If you have noticed that it takes a while for the attack animation to start after you click, here's a fix:

As the title suggests - You don't need to download anything.
If you wish to use something like AutoHotkey, there are guides available for that.
With this solution, you might have to click 6 times every time you launch the game... Which to me, at least, is easier than dealing with extra software.

While in-game, open the key bindings menu, and switch "disable double clicking" to ON. Keep reading!

The next time you start the game, the delay may come back, so you have to switch "disable double clicking" off, and then on again. You will know it worked if you got a pop-up telling you that double clicking will no longer work.

You will no longer be able to double click for heavy attacks, but I would not recommend using that binding in the first place.
Last thing you want in pvp is to get stuck with a heavy attack animation instead of normal.
Set it to an easy key, q or e, or 2/3 which is right above the w and not occupied by anything else.

PS: I don't know if anyone's posted anything similar. At least I haven't found anything on it when I was trying to deal with the problem. And yes, pretty sure EVERYONE who's reading this is aware of the existence of controllers, you don't have to make that comment, thanks. :P

If this did actually help you, please give it a rating. If I'd found something similar, it would have saved me a few hours of headache.

Edit: I came across an awesome overall pc controls guide: http://gtm.steamproxy.vip/sharedfiles/filedetails/?id=423591399
While my post covers just the attack delay, this guide provides tips and solutions to many more things as well! If you're new to the game and use KB/M, I highly recommend checking it out!