Here is a pretty good example of a very large trained fighter and a very excellent and much smaller tai chi guy going at it reasonably hard (like maybe one of them walks away with a concussion type hard).

https://www.youtube.com/watch?v=7D5DGpORANE

I think that's a pretty good example of what "people who can actually fight well use tai chi techniques" looks like. A lot of force is going into those throws, bodies are flying, and they aren't students doing a demonstration for a crowd. Legit.