I think you should incorporate N-Acetly Glucosamine into the niacinamide toner. They apparently work together to create better results, as somebody else on EDS forums has the same problem and used this combination to fix their dehydrated problem. Interesting stuff about the epidermis, but having lots of skin cells forming barrier could prevent the absorption of niacinamide and perhaps getting a gentle microfibre cloth to exfolate might work better for that absoprtion. My advice is, if it looks worse, the product is not helping. However, when i exfoliate gently, it makes the skin look slightly better. If it doesn't look worse, i think that its not doing harm and could perk you up a bit.
I am too suffering from what you describe. Mine came about when i used a cleanser for acne that you have to leave on for a few minute before washing. It has all the hallmarks of bad advice, as the cleasner contains sulfate and an anti-baterial agent that i think was the cause of my problem. Basiclly i have dehydrated skin, like yours, and you can tell because it looks drained, has no glow or moisture to it, doesn't moisturize at all by using any cream or lotion. sometimes it can be oily, but not by much. My skin can sometimes look somewhat polished on my cheeks when it gets bad.
Could you describe what the rest of your facial skin is like?
I am going to do the same thing as what you are doing with the DIY toner. I also wash my face with Cerave hydrating cleanser. It doesn't make it worse and washing can be somewhat good as the barrier can still hold some water. If i did not wash for a week it would just look worse because there would be a severe lack water in the skin. I also finalise by using Cerave PM. It has ceramides, niacinamide and cholesteral in it. It's meant to be good for this sort of thing, but i have regreatably not seen any miracles or good results with this product, although i have only used it for a month.
I hope things get better in the end for you.