I can only tell you about my own experiences in this area.
Since being diagnosed with primary hypothyroidism 17 years ago (autoimmune hypo-T or Hashimoto's disease), I have read that you should take T4 only, mostly T4 and a little T3 (to mimic what your own thyroid gland would be giving you if it was healthy), NDT (which contains T4 and T3 but in different ratios than the human thyroid gland would produce) and, finally, T3 only.
If there is one thing I've learned over the years, it's that we are all different. That may sound both obvious and ridiculous, but honestly...how many diseases are there where you have so many patients doing well on so many various treatment options...? I mean, how many people suffering from hypertension, epilepsy, diabetes, or RA, just to name a few, can try so many treatment options as we do before settling on one...?
I will probably never understand this fully, but I know, after reading literally thousands of posts over the past 15 or so years: some hypothyroid people will do perfectly fine on T4 alone. It's important not to forget those people because they do exist. I never did fine on T4 alone, but I know people who do.
However, even though I never did well on T4 only, I have never been able to wean off T4 drugs completely. I know people who have stopped taking T4 altogether, taken T3 only and done great.
To sum up, I never felt optimal on T4 only, but I never did well on T3 only either. Since realising this, I have tried to find the optimal T3:T4 ratio for me...I'm still not there, I'm afraid. I'm beginning to realise this may be due to estrogen dominance caused by estrogen supplements well before menopause, and this in turn will affect the body's ability to effectively use thyroid hormone.
I think you should not obsess too much about what you should take and how much; rather accept that you seem to need some T4 as well, and take it from there. What I mean is: try to figure out the ideal T3:T4 ratio for YOU.
When you visit a lot of forums and blogs, it's easy to get the impression that T4 is a useless hormone only meant to be converted to T3, so you might as well take T3 directly and forget about T4.
That sounds easy, but if that is how things worked, the human thyroid gland would only need to produce T3, and no T4...if it does in fact produce 80-98% T4 (that figure will vary depending on your source, but you get the picture), that is because, in a healthy body, T4 does have a role to play. Of that, I'm sure. And, like I said, although T4 alone never worked for me (I continued to put on weight, feel tired, look puffy, have heavy periods, adrenal fatigue, just to mention a few side effects of thyroxine only treatment), T3 alone never worked for me either...it's obvious to me I need both T3 and T4, and I am currently trying to figure how much of each.
That may very well be true for you as well, so don't give up; it can take a lot of time and patience figuring it out, but please don't dismiss T4 as completely useless and dispensable.