Back when I was a college student in the 70s, when I first got interested in Chinese Martial Arts, I hung around with some oddball new-agey types who were into beating drums, yoga, tai chi, and a moderate amount of substance abuse. I remember getting a book on Yang style done for health by Herman Kaus (?). I began training a semi-phony, chop suey shaolin system that pretended to teach some tai-chi. Looking back, I'd bet the Shifu's Tai chi was out of a book too. He was also into "Transcendental Meditation"...remember that? At that time it seemed like every Kempo and Kung-fu school taught some BS tai-chi as a "part of their system". You still see that a lot of places, even today. LOL.
Anyway, I finished school, moved back home to Arizona and stumbled into Wing Chun. I also had a bad accident that caused traumatic arthritis and severely restricted movement in my left ankle. That on top of a congenital condition that already prevented lateral flexion in my ankle joints. I was still able to do WC with a compromised stance, but Tai-chi was out of the question. Every time I bend my knees and sink my weight, my left heel comes up off the ground, and it hurts too. You can't do tai-chi teetering on your tip-toes, tensed up because you are in pain. So from that point on, my interest in tai-chi became purely that of an occasional spectator.
I will say this. I've met a lot of new age health fanatics who love tai-chi, but never move beyond doing the forms slowly. No push hands or sparring. On the other extreme was a guy name Michael Leung who owned a Chinese restaurant called the "King Wah" and taught a few Chinese kids after closing, out back behind the overflowing and foul smelling dumpster. One of those kids was a Wing Chun buddy of mine as well as this guy's tai-chi student. Furthermore the instructor, Michael, was somewhat in awe of my famous Sifu from Hong Kong, so I was the lone "gwai-lo" invited to watch or join-in and spar. These guys didn't spend time on forms when I was there. It was all fighting. I saw plenty of bruising, busted lips, and bloody noses. It was definitely a martial art and not at all "new-agey"!
Along the same lines, when I was starting out in WC/WT in the early 80's, I remember foolishly asking my old Chinese WT Sifu what were the most effective martial arts besides his own. At first, with truly classic arrogance he dismissed the question saying that of course his art was the best, and that was that. Otherwise we should stop wasting his time and find another sifu. Still, I pressed the question, asking that, supposing his art had not been invented, what would his second choice of martial art have been? He paused, and then said, "That's easy. Tai-chi. Not the tai-chi you think of. The real fighting tai-chi. But you don't know about that here in America."
So I guess I don't really know what tai-chi is at all. It seems to change a lot with who's doing it and what their objectives are. Now Xue, stop holding back and enlighten us. We know you've been at this for a very time.