For what it's worth, here's my 2 cents. I won't bore you with my long history of internal arts study beginning with Ki Aikido when I was about 25. But eventually I found an interesting teacher of Wu Taijiquan, named Dr. Stephen Hwa. I know some of you are familiar with him, but I don't know how much you've looked into his teachings. He spent decades studying from Yang (Young) Wabu.
To give some historical context, during the tumultuous period of war breaking out with Japan in the late 1930s, Wu Jianquan lived with Young Wabu at his home in Hong Kong for a couple of years. Young learned and practiced Wu Taijiquan with Wu Jianquan day and night during that time. Young was an accomplished master of external martial arts before he met Wu Jianquan. After being defeated by Master Wu, Young decided to devote his life to Wu style taijiquan.
You can read more about Yang (Young) Wabu here -
https://www.classicaltaichi.com/about-t ... sters.html and here -
https://fliphtml5.com/zbap/atuw/basicMaster Hwa also has a YouTube channel and lessons on Teachable under Classical Tai Chi. He also has some DVDs for those of you who still have DVD players, and he put the entire square form, move-by-move in PDF form that you can download for free if you're curious. He is a very brilliant and generous teacher. At one time, he was willing to go out of his way to meet with me in Pennsylvania when he was traveling through the state. I regret missing that opportunity. He lives in Florida now and as far as I know, is still going strong at 90. His teacher, Yang Wabu lived to be 101.
Master Hwa said that the square form was not taught to just anybody in the past, it was a special form reserved for inner door students. The main reason for this had to do with the fact that it ensures precision of movement, so the form does not get altered or diluted over time. Wu Jianquan told Young Wabu that the form he taught to Young was exactly what the Yang's (Luchan and Banhou) taught to him and his father. They did not change the form, as it cannot be changed without altering the structure and weakening the usefulness of the art. Some people would agree with this as some have said that if you want to learn original Yang style, learn Wu style. Especially since the form taught by Yang Chengfu is said to be different from what his father and grandfather taught. It is known that Yang Luchan and Banhou preferred small circle over larger circles and frames. The small circle Yang form done by Vincent Chu does seem to have some similarities, at least externally, to what Stephen Hwa teaches in the round form. Master Yang Wabu was a very strict teacher, who only taught his students Square Form, until they were proficient, at which time they learned the round form. The Square Form is a template for the round form. The basic round form would be learned more easily after mastering the square form, but that's just the beginning. You have the rest of your life to then improve the round form and learn what Master Hwa calls "internal discipline" as well as learn push hands, weapons, etc.
The other point of square form brings me to my next point. Taijiquan is the separation of Yin and Yang. Forget about all that grand ultimate fist stuff. When Chen Wanting started it, he was a Taoist and wanted to implement ideas of Taoism into Taijiquan. It's right there in the name. You cannot have Taijiquan without the basis of it, which is separation of Yin and Yang.
In the Wu Style Square Form, as taught by Stephen Hwa, it is very important that your body remains perfectly Yin, or still, except for the Yang part, which is moving. Only the Yang part should be moving. Nothing else. Yes, this ties in with what Master Chen Zhonghua teaches in Chen Style Practical Method Taijiquan. I have not yet met Master Chen, but plan to either this year or next, as he regularly comes to NYC to do workshops. I did however, take a private lesson from Michael Calandra, who is a long-time student and disciple of Master Chen Zhonghua. I also own about 100 of Master Chen's videos. I'm far from understanding much, but I think I get the core principles. Doing it correctly is another matter altogether.
Master Chen certainly emphasizes this separation of Yin and Yang in his teaching. You cannot have power without it. If your whole body is moving, or you're moving things that shouldn't be, we call that "tossing". Master Chen repeatedly tells his students "Don't move". It's hard to grasp and people argue with him because it's hard to tell that you're moving. Practical Method can certainly look robotic, especially when you're first starting. This is where beginners in Practical Method certainly appear to be doing a Square Form, similar to Wu TJQ square form. It wasn't meant to look pretty, it was meant to teach a body method to work in combat and it just happens to be great for health and fitness, as many of these arts are. Master Chen has mentioned that he's not just teaching a martial art, he's teaching a body method. You can do more with that than martial arts. One of his students used it to improve his tennis game. Ironically, Master Hwa mentions how TJQ improved his tennis game, as well.
I could go on and on about all of this, but in my opinion, there is what I call a "golden thread" that weaves all of these Taijiquan forms and styles together. That starts with separation of Yin and Yang in your movements, but there is much more there that I haven't uncovered yet as far as what is familiar in different styles of Taiji. Yes, the forms look very different. Nobody really knows exactly what Chen Changxing taught to Yang Luchan, but it's not too hard to see similarities between the styles if you look for them. They may have changed a bit over the years, but I still believe that really good Taijiquan has survived at least in principle, even if the forms have been altered a bit. Some styles seem to have lost some important material, but it's worth discussing and checking our ego at the door if we want to understand and improve. I am not knowledgeable enough in Practical Method to know if you work towards a smaller frame when you become more advanced. I would like to ask Master Chen about this someday.
I may be wrong about all of this. I'm no master or expert. I'm just a ham and egger who has had a lifetime interest in martial arts and enjoys practicing for the health benefits, fitness, mental exercise, challenge, and fun. Please don't take my word for any of it, but look into what these teachers have to say and form your own opinions. You may have to spend a few bucks and some hours watching their videos and reading their articles. You shouldn't form an opinion on most people based on one or two YouTube videos. I do know that these arts are hard to grasp and very difficult to do even somewhat correctly. Enjoy the journey.