For me, texture plays a larger role. In the winter, my hair cannot stand any protein at all, and my hair is quite porous. It's instant hay hair. I do better with moisture and sealing. I think that fine hair of any porosity is more tolerant to protein than coarse, porous hair.

In high (65F and up) dew points, my hair can handle protein (keratin only) in decent amounts. I think that, for coarse hair, protein isn't always the best way to deal with high porosity. It can't be 'fixed' the way some protein treatments claim to fix it. If it's porous due to damage, damage isn't fixable, just bandage-able. If one is naturally porous, nothing is changing how it grows out of your head (hormones and medications excluded).

I just feel that sealing can be just as or more effective for dealing with porosity than protein is, especially in low dewpoints when coarse, porous hair needs a lot of moisture.
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Med/Coarse, porous curly.