I appear to be killing everyone with one swipe of my sword. Last time I played this game the prologue was a challenge.
I recall having to hit a soldier twice or three times to take them out, now I just hit them once and they're down.

I have the Enhanced Edition 3.4. Not using any mods.

Are you at the very, very beginning or what? If memory serves, there's a fake battle scene in one of the vignettes where you don't actually have to do anything, but if you do swing your sword, everyone drops in one hit. Maybe wait it out a bit?

Did you use any mods at any point before? Sometimes if they don't get deactivated properly they can still mess up the combat.

Your memory is correct, it should take several hits to kill enemies in the prologue.

Okay it seems to be because I started playing with a FOV mod. Even after turning it off and continuing Geralt was killing with one hit (including the practice dummies!). So I started a new game without the mod, saved, quit, turned on the FOV mod and reloaded my save and now killing is working properly again.

Weird.

Glad you got it working!