Tai Chi is a martial art performed in slow motion. Sped up it is very effective and deadly.
TMAs are more romantic than effective. The entirety of the 90s showed us that. The Chinese, however, are stuck in the past. They don't like their traditional arts being shown up for the paper tigers they actually are. Basically, they got left in the dust as the rest of the martial arts world passed them by.
Effective martial arts (which stood the test of time):
- boxing
- wrestling (catch or greco roman)
- judo
- jiu jitsu
- sambo
- Muay Thai
- karate
These arts are what the top level guys are all cross training in. You need decent striking and grappling. A lot of guys are mixing up Muay Thai and wrestling or jiu jitsu. If you focus on jiu jitsu for grappling, you need a decent takedown game because jiu jitsu doesn't really emphasize take downs. You'll see a lot of judo guys take up boxing as their striking, because judo is terrific for takedowns and has decent grappling. As you can guess, many D1 wrestlers who take up jiu jitsu find themselves advancing fairly quickly as soon as they get the muscle memory to disregard wrestling rules. Throw some boxing in the mix and you got yourself a deadly fighter.
Just watch any video with a Tai Chi master (or whatever TMA master) go up against a modern fighter. I wouldn't really call Tai Chi effective or deadly. It's possible that it could've been those things back in the 19th century.
It'd be akin to Floyd Mayweather fighting this guy:
He might've been a tough dude back in the day, but there's just so many techniques now. It's an outmoded way of fighting.
I'd use TMAs more for physical exercise. I guess in an absolute pinch it'd be better than nothing at all.