Free Step Dodge

I ask because in the DLC the mechanics of how the stances work seems to be collapsing...

Do you mean the situation for when you stagger as when you are making attacks?

So to poise through attacks (or armor through them) you'll have to raise your toughness stat (which is mostly pointless on higher difficulties) due to some enemies/boss having various attacks that can one shot you.

Toughness also varies for the type of gear you wear. Having extremely lightweight armor provides you with very little toughness, whereas wearing heavy armor (such as Tatanashi) provides higher stats on toughness.

A common question that people once asked is that why some enemies don't flinch as often when you attack them (especially heavy build revenants), is because of their toughness stat or wearing heavy gear. If a revenant is tanking you while he doesn't flinch, that player likely was wearing heavy gear that raised it's toughness a lot.