Another 2 cents here. First, your position HAS vastly improved though it is interesting to read you think it has gotten worse. In the pics for three years ago you had a very textbook beginner with little to no training style..I know..I had that same style. In the second set of pics, as indicated earlier, you were standing in your irons which pushed your upper body forward..not unusual in a green jumping style. This was due to not dropping the weight into your heel and not folding into the 2-point. Your release looks to be more of a hands on neck open release (note straight line from elbow to horse's mouth) vice the crest release I think you were actually trying for. Resting the hands on the neck is a classic out-of-balance or no balance red flag.
In a crest release you would move your hands up the horse's neck and rest on the top..not down on the side. IN an open release your hands are already in the right position (even if by mistake) but you would not be touching the horse's neck with your hands. In this article, look at George Morris for the proper crest release..not the other rider. The article greatly over exaggerated the issue with a crest release as that particular rider is not in the proper form in any way shape or form of two-point and definitely not a form that is actually taught (if she was taught that position then her trainer needs to be fired). Horse jumping release: The crest and automatic release in jumping
Some ideas..and some of these are repeats :).
1. Lots and lots of flatwork 2-point. An instructor I had in Louisiana had us do nothing BUT trot two-point for the first 15 mins of each lesson..and yes she timed it. I rode with her for three years; the first 4 months I could barely walk after dismounting. After that time, however, I had the strongest leg imaginable and my two-point was rock solid. The idea, however, is to do a proper two-point. Weight in heels, shoulders back, head up. Fold at the hip..picture in your mind pushing the horse away with your hands (both on the flat and while jumping). This helps you get your hip in the right position and keeps your weight centered.
2. As for holding two-point to the base, this isn't a bad thing when working on balance. The idea there isn't to just get in to two-point but keeps the inexperienced (or just relearning jumper) into position early to keep from getting left.
3. Exercises through a small grid (crossrails or tiny verticles set at about high cavaletti height, 12 inches?, holding arms out to the side will help.
It is not a bad thing to go back to the low basics. I've been riding for over 30 years and jumped a good 25 years of that (dressage only now). All my trainers at some point took a week or two every 6 months or so and brought us back down to basics....back on a lunge line if we ended up alone for whatever reason or doing those simplistic grids etc. This happened more often if the class was getting cocky and the jumping position was beginning to suffer.