If you're not chemically processed then wear and tear through washing, using brushes/combs and normal handling can still cause cuticle damage, also of course drying through heat with blow dryers. But yeah, surprised it is so brittle. I would hazard a (very uneducated since I haven't seen your hair in real life and know your routine) guess that your hair is dry and needs a lot of moisturising, but also needs some protein. In fact that the introduction of protein may help it to use and retain that moisture. I am writing this to myself as well as you!!

So yes, go for it with protein - if you are interested in CJ Repair me it is a protein treatment that is also moisturising, still follow with a bit of moisture too though. But also, don't let up on moisture as you use protein - ie. follow up protein focused things with more moisture, don't suddenly use protein every day, still do your weekly JCWDT with heat. I really think we need both and maintaining moisture as we introduce protein will be quite key to success. So maybe you could think about doing some co washing, always using plenty of moisturising rinse out (sounds like you do already but not sure how much you slather on), and going for a higher moisture leave in if needed. I haven't used KCKT but I have heard it is more of a slip detangler than a moisturiser.

I bet you'll see really good results soon , I'll check back because I'll be trying the same kind of things. But, with my large chemically damaged sections I probably will need a big haircut before I really see those results. Must get to that, but that's another story
UK based wavy

Mostly waves, but curls and straight bits too!
Fine to medium, high porosity, medium density, very low elasticity
Highlights damage (growing it out), seems to like protein and need lots of moisture.

Cleanse - CJDF, trying out low poos ; Co wash- Uk chemist brands, Urtekram Rose or Aloe, Hairveda Amala Cream Rinse; RO - varies, Tigi Moisture Maniac, Desert Essence Coconut ; Leave in - Keracare natural textures; Sealant - argan oil
Trying out new things, still looking.