It’s more like agility than traditional poise
After Bandai Namco and From Software were wholly unhelpful when it came to explaining what the poise stat does in Dark Souls III, a community member may have just figured it out. According to redditor Back_Like_Flint, it actually has to do with rolling animations, and not stagger deterance and ability interruption.
In fact, it’s more linked to agility than anything as it influences invincibility frames during rolls. Flint breaks it down much further in their massive tome on the issue, which seems to settle the debate once and for all. Yes, a fan actually broke down and tested various poise ratings frame by frame over a month out from the game’s launch, because someone, whether it was the publisher or developer, didn’t want to explain the stat themselves.
Modern gaming is weird!
Dark Souls 3 Poise Mechanics [Reddit]