HP and extra armour are pretty interchangeable for IF. I think something else should be changed regarding it.
Right now we have for strength: Power skills, Iron Flesh
Agi: Athletics, Weapon Master
Weapon master got buffed, increasing the distance in wpf between WM levels, and agi also governs shield and riding as well. Since you'll hardly ever get more than 1 power skill at a time, it's PS & IF vs ath, WM, and possibly 2 other skills. Out of the skills listed, IF just ain't cutting it for being nearly as useful, while PS/Ath are equivalent.
WM let's you swing better and gives you some damage. I was thinking letting iron flesh let you hold attacks better while increasing hp (yes, I compare the hp bonus to wpf's attack bonus), decreasing the drop off rate in damage for holding. Makes sense all around to me without overbuffing it or anything. Strength builds can't spam and rely on holds, so it seems to me like it would intrinsically help out.
Shield makes sense, but I do not think items can have multiple requirements like that. I also don't see much of a problem with <13 strength shielders considering high shield skill was nerfed, so axes are going to break them quite quickly compared to before. They're already limited on almost all other equipment what they could use.