Poise is a defensive stat, if most enemies ignore it then you are wasting your weight allocation (and by extension, your investment in stam)
Ppl testing poise against enemies you meet in the first ten minutes of the fucking game is stupid as fuck, Youwy actually tested it against tough enemies and it's borderline useless
Damage mitigation is another matter but in most cases tough fights are not won by mitigating damage through armour
By far the best strategy is to avoid getting hit in the first place or to block hits using shields, if you are regularly taking damage from non-boss enemies then fine but at least get 55+ poise or its completely fucking useless
As for bosses, they pretty much won't give a fuck about your poise, damage mitigation is somewhat of a factor versus bosses but the equip load investment for some of these armour sets is so insane that you're better off using high vigor to soak damage from your mistakes than high armor (via high stam)
Not to mention that a lot of damage mitigation strategies versus bosses barely rely on high armor at all, armor is just one small piece of the puzzle, the other pieces being consumables, spells, etc, and by lowering your armor you are still able to create a highly effective damage mitigation strategy because return on investment with heavier armor pieces is absolute shit, the most valued items are stuff like crab meat giving you +20% mitigation etc