Unless you've already trimmed/cut off all the chemically processed hair, I wouldn't assume it isn't playing a factor. If you have, great. If you haven't, you might want to trim or cut it now. Even something as mild as a demi-permanent color process can make hair over-porous and prone to all sorts of problems.
An ACV rinse (directions can be found on site) often works to restore pH balance, so you can first give that a try, but I doubt that's your whole problem.
I agree with you about checking your hair's properties, porosity in particular. Since you said you've lost elasticity, sounds like protein is probably not the culprit, but SpiralSpunk could be right and I could be wrong. Here's something you can do to try and figure out whether you're on protein overload, or need more moisture: First, do that clarifying wash to get everything out. Next, take a few samples of your hair from different areas of your head. DT with a quality conditioner that contains no protein. When done, take more samples of your hair. Is there more elasticity in your post-treatment hair? Less? The same? See how the hair on your head responds too.
A telltale sign of over-hydrated hair (hygral fatigue) is your hair will take even longer to dry after your DT, and it will have lost elasticity with "wilted" curl. It may also feel "spongy" ... If you see little to no difference w/this experiment, try another protein treatment - a serious reconstructor, like Aphogee or K-pak, leaving it on for 15-30 min.s - and repeat the steps above (hair samples) to gauge changes. A protein reaction includes stiff, dry hair that feels brittle and may even break off in places. So if it feels even more stiff and dry, protein could indeed be the culprit and you'd need to back off from that for a while until your hair is more balanced.