So while experimenting with parries and fighting with the weapon sheathed... I realised a well timed attack as you're parrying will perform its own unique follow-up which has the same diagonal cut kill animation as the (missing on the downloadable version) second combo attack.
So all the combo attacks have a second way to get the same kill animation.
That makes sense. If you can only counterattack off the final hit in an enemy's combo, that's already consistent. It's just consistent in a way players will learn over time. A lot of games have mechanics like this, or ones where you can counter some enemies anytime, but others only off certain attacks.