And it is known that Chen style incorporated pre-existing martial arts as well.
Luchan was said to be Yang Wu Di. The Chen family held him in high esteem. His art is not the same as Chen and considering the respect and skill he had they should not be compared so flippantly. There are several claims that Yang style is based on principals he obtained from Taoists.
Chen style training is however something we can assert Luchan to have gone through, and clearly to have benefited from, but if we esteem this fellow let us note that he underwent more than one type of training, and thus was not a product of his own system, he was the author of it and was the product of multiple systems.
All of our styles try to adhere to the Principles of Taijiquan set down by our Masters. So what if our Forms are different. Applications may change, depending of the pracitioners mind. The Forms change accordingly. But, do the priciples change? Can you apply them..that, I think, is what is important.
I agree that form can vary, but can application truly change and the art still have the same title? The title itself is the most sublime application instruction possible, applications are endless, but are based on basic concepts, rather than specific responses. however that is for the art I was taught, others have traditional set applications said to hail from the Yang Family, like the Mi-quan tradition.
I discarded the forms I was taught, but drew from them. They read like a book, but one that has had pages torn out. I went back to the basics and condensed everything into a training regime for myself, including with very simple forms. Of course this is not for others, I simply know what kind of skill I want and engineered exercises to obtain it, if your teachers students have the skill you want then they are good teachers. If your teacher has the skill, but his students do not, or very few of them do, they are a poor teacher, despite being a good martial artist. Test taiji teachers this way and no other, their skill and knowledge mean little if their students do not readily obtain them.