No, there's not really a thing such as protein deficiency, I think, as protein just makes up part of hair structure and using protein products is just a poly filler to repair wherever that structure is damaged but that washes away. In that context I think with protein deficiency it just means damaged hair. I'm not sure if that counts as frizz.
Frizz is, as I understand it, is solely a dehydration issue (it's skincare all over again, I don't have dry hair, I have dehydrated hair, I already sort of knew this but nice to have confirmed) and on a more science nerd level it's about how hydrogen bonds to the hair's own protein and distorts it (see pic with explanation, I'm still digesting it).
Thing is, I'm not finding much information on what you can do to help with dehydration. There's a lot of standard advice about sealing in with oils but that only works if you're also dry. Then there's Humectants plus sealing it in with lighter ingredients like film formers, cationic compounds, silicones, lower weight oils, etc.
The only lead I have is inositol (in rice rinces) as that hydrates and penetrates deeply but it can't be the only ingredient that does that.