Alright, I finally had time to load in, swing around a bit in a room at different timings with different swings. It mostly felt alright between the timing of heavy attacks and quick attacks, but I was still occasionally getting weird hiccups in the swing rhythm that would occasionally throw off what I was expecting. Slightly annoying but not as annoying and jank as it had felt when casually playing.
As soon as I then mindfully found something to bash and paid attention to the flow of it, I think I figured out why it feels as off and jank as it does.
Specifically it is the case of starting a fight with a fully charged swing ready, running up to an enemy, and then immediately trying to follow it up with a short quick swing. Which I'm going to guess is an incredibly common melee cadence that people default to wanting to do. In general I'm guessing most people default to either that, thwack once and fully go to dodge, or repeated heavy hits while not caring about retaliation.
The problem with the charged attack from the right followed by trying to short swing after is that the follow through of the first hit is way longer than it feels and for a lot of that time even a short click will immediately transition into getting into the stance for a two hand full power swing from the left. What feels like "I input a short click" is being played as what is expected for "I held down for a moment". It also seems that the following hit, from left to right, doesn't have this problem on quite the same level. This adds up to a lot of fights having an awkward second swing but then you switch into the quick attack rhythm for the third and following.
So the confusion and feeling of jankieness is, I think, entirely coming from the melee combat equivalent of a single quarter note in a short jingle you expect to know being replaced by a half note, or the second stair of a staircase being an either of an inch off. Everyone just keeps on tripping and they don't quite figure out why.