To gain the full health benefits of tai chi, you must make it part of your daily life.
It was designed to be a tonic, not a solution/cure.
Weekly class practice is fine, but daily tai chi offers a degree of suppleness, strength, mental clarity and flexibility you are currently unfamiliar with.
Martial artists are another matter entirely.
Muscle memory and reflex must be cultivated and trained continually so that the body simply responds habitually.
This requires heavy repetition, practice, homework.