Game Mechanics: Two Hand Blunt Max Weapon Damage (Monk)

[kanras]

I assume PWR = some calculation of attack and strength.

PWR is the portion of displayed ATK that relates to damage calculation after a hit has successfully landed. The other portion of displayed ATK is ACC which relates to your chance to hit. Yes, STR has an impact on PWR.

Unsure how the minimum damage is 19

If you look at live parses where high damage (15+) weapons are used, you'll see that:
MIN_HIT = DMG_BONUS + MAX(FLOOR((WPN_DMG+5)/10),1)

So for your poly axe, it's 15 + FLOOR((37 + 5)/10) or 15 + 4 = 19

54 Paladin using Polyphenomenal Axe (37/48)

All classes besides war/mnk/rog/rng still use the (STR + OFF) / 100 to calculate their max damage multiplier post-50.