There is no documents of any kind related to Yueh Fei having attained any mastery of empty handed arts (yes, I know that as a soldier he of course was going to be well versed in some type of hand to hand combat, Shuai Chiao is very possible), but at that period warfare was more done with spears, bows and arrows and other type of projectiles and long range weaponry.
Xing Yi is said to have developed from armed methods not the other way around. My school teaches traditional weapons (as well as archery) and we are always told that the weapons would have held greater importance than unarmed methods in the past. TYhe main weaponof Xing Yi is spear. It si interestign if you have been taught traditional weapons such as spear or zhanmadao (horse chopping sword) that these methods link directly back to the Sung dynasty when the chinese were fighting Jin/Kin (nomadic northern tribes known as the Jurchen who were not at that time ethnic chinese and they broke the northern sung dynasty captured Kaifeng and started their Jin Dynasty), for example why have a "horse chopping sword"? The Jin were nomadic horse archers and lancers, the northern steepes were the traditional horse breeding lands. The chinese had relatively few horses due to the loss of northern lands so Yue Fei developed infantry tactics to beat cavalry using spears, pole arms and specialist weapons. There are weapons techniques in Xing Yi to dismount cavalry, disable horses, pierce armour etc where did these come from? Not from anyone after Ji Long Feng as there were few pitched battles on the same scale using these types of weapons (superceeded by firearms) during the Qing dynasty. But these traditional strategies wouldn't have been forgotten by Yue's close colleagues and family who served with him. After his murder (killed awaiting trial for treason) his family and close officers fled and hid, China is a big place so it isn't so hard to believe that a family art and tactics held by key persons stayed hidden so long. Yeu Fei was demoted yes but I heard this was due to the corrupt government, the Jin payed off officials to discredit Yue, who stood in their way.
He was demoted a number of times and eventually charged with treason; despite commanding an army large enough to take the Sung Dynasty or his own Yue traveled back to the capital and awaited his trail despite knowing the risks. By the way Yue Fei become a national hero after his death, he was given a traitor's burial and only many years later did the government back down and the emperor ordered a new tomb be erected to Yue Fei (which still exists). Just to reiterate also that the Juchen who he was fighting were not a Chinese minority but a state and people of their own (this is well documented), maybe they are thought of now but apparently anyone who lives on lands which were at one time Chinese is a Chinese minority, something I think at least the Tibetans and Mongols might disagree with of not other groups.
Anyway I didn't say Yue Fei created Xing yi in my post. Look carefully, read it properly, I labeled it as a
standard lineage down to Li Cun Yi you can find this from many sources. I've given the name Yue Fei as a possible starting point, from which the armed methods of Xing Yi may have had some influence from and I have noted that there is no documented link for approximatelty 500 years. As far as I'm aware there are still people in the area of Zhongnan Mountain who practice Yuechiaquan so there may be a link between this and Ji Long Feng. Its all half truths and speculation but you can see the same threads in most linages people tell so there has to eb something in there. martial arts aren't often plucked from the ether and created on the spot, they are evolutions of earlier ideas and methods. I believe it is liekly that what we call Xing Yi came from weapon based tactics developed in the Sung Dynasty
Ji Long Feng is (as far as I'm aware) the first documented Xing Yi practitioner and likely to be the founder of what we would call Xinyi. As far as I'm aware Cao Ji Wu is documented in official records as he ranked in the imperial martial examinations and was given a post within the military/local government. I can't confirm this, its what I've read and been told. If you have convincing arguements otherwise let me know.
Take for example, how could a style remain hidden for 500 years? this is impossible. Practitioners were/are proud of their arts and would like to at least made it clear that what they do (Xinyiliuhequan) is unique and worthy of recognition.
People hide things for a number of reasons, most of all self preservation. There are hundreds of family styles in China which westerners have probably never heard of, China is bigger than Europe so its quite easy to think that actually a few people scraping existance in a mountainous region of shanxi may not have shouted from the rooftops that their art was number one, and even if they did maybe no-one heard them. Xing yi developed in Shanxi, Henan and Hebei provinces, until recent times half of China proabably didn't know or have access to people who taught Xing Yi, and how many people in the west have access to good Xing Yi? There are chinese masters that don't teach openly too,there are probably lots of very good xing yi guys in china who do not teach openly and people have never heard of them.
At the end of the day it comes down to what you believe and what you discount. If you dismiss everything without looking closely then of course everything is ridiculous and your teacher knows best. I'm interested in the evolution of the art from what it was into what it is now, most people think it was always how it is and everything comes down from one source - life is more complex, maybe Dai long bang learnt from Coa ji Wu, Li Zheng and the Niu family as well as his own familiy styles? Maybe his xinyi was a fusion of these? Ji Long Feng had already been in the Ming army and was an expert with spear before he created Xinyi, what other influences did he have? We can never prove these things but maybe people have different views This is the kind of thing I'm interested in finding out, I'm no expert but I'm not discounting anything either just because my teacher may have told me something this way or that way.