How does Yang taiji compare in terms of focus and philosophy? I ask because it is said that Moo Duk Kwan GM HWANG Ki spent time in Manchuria and learned that from a Master YANG Kukjin.
Depends. I'm not really up on Yang except for the generalized history about after Yang Lu Chan left Chen Village & went to Beijing. He watered down what he learned in Chen Village to prevent the Qing's, who were paying him at that point for martial arts, martial arts. There are lineages of Yang that while maintaining the less overtly martial appearance of Chen, are just as mean & ugly as Chen when hands are touched. Those lineages tend to be found from adherents of the Yang family directly, not so much students of students. I could be very off on this due to my non-Yang background & lack of Yang research.
Yang however is also the most prevelant to have people practicing "Tai cheeeeeeeeeeeez" as opposed taiji quan, that is to say no martial content at all while trying to hug the universe.