I've been following this thread because I'm having similar issues and I think my hair properties are close to the OP.

Firefox - your explanation matches my experience. My hair was curlier and less flyaway after I did the gelatin PT, but it didn't last. I feel like I need to do another one after only a couple of washes.

I guess the right thing to do it use smaller amounts of protein in more products and/or do longer treatments with protein or coconut oil. I might have to try overnight coconut oil again, but with much less oil next time.

What problem did you have with cetyl esters? Is that the same as emollient esters? If so, Tonya McKay mentions them as a potentially problematic occlusive agent in this article:

Hair Moisturizer vs. Emollients
Originally Posted by CurlyGrey3
Cetyl esters are indeed an emollient ester.
Cetyl Esters-Conditioners, Thickeners, & Structural Agents-Home-Blending Nature and Science - Innovative Natural...

My curls were poorly defined, weighed down and totally limp IIRC. Initially I thought I was overconditioned which seemed strange given I have damaged porous hair, then read the conditioner ingredients and found amodimethicone and cetyl esters. Shampoo'd with cocoamidopropyl betaine and hardcore protein treat which my hair HATED, but it's worked out for the best, I've learned my hair likes proteins in an emollient/ conditioner base much more than the hard drying type treatment.
2a-2c, medium texture, porous/ colour treated. Three years CG. Past bra strap length heading for waist.

CO-wash: Inecto coconut/ Elvive Volume Collagen
Treatments: Komaza Care Matani, coconut/ sweet almond oils, Hairveda Sitrinillah
Leave in: Fructis Sleek & Shine (old), Gliss Ultimate Volume, various Elvive
Styler: Umberto Giannini jelly, Boots Essentials gel
Flour sack towel, pixie diffuse or air dry.
Experimenting with: benign neglect