Some martial arts classes serve to preserve and safeguard an art that would otherwise die out.
Swordsmanship, archery and other such practices have little purpose in modern life.
The students who train these arts keep the knowledge safe.
They preserve the heritage.

Are these viable martial arts classes?
On the one hand they are; the skills are genuine martial skills, no doubt proven in actual combat over many years.
On the other hand the skills are not functional or viable in modern society.
Will you be carrying a sword?
If you did carry a sword, are you legally allowed to use it?

Fighting groups do not really constitute sport because their aim is not to compete.
The aim of a fighting class is to engage is combat that is as real as possible.
In this regard, such classes are following the martial spirit.

Unfortunately, brutality and strength often prevail.
A student may suffer more injuries in class than on the street.
In such a class, the artistry of the martial arts takes second place to guts and sheer determination.

Many martial arts have become sport.
Instructors are now 'coaches' and the whole approach is geared towards competition.

There is nothing wrong with this, if this is what you want to do. 
However, strictly speaking, such practice constitutes 'sport' not 'martial art'.

The mandate of sport is quite different to that of a martial art.
Sports are about winning and losing, gaining trophies, medals and awards.

At its most crude, a martial art is simply about surviving a violent assault.
At is most refined, it is about attuning yourself to the way of existence, adjusting to the rhythms of life.
No sport can offer this.

Tai chi is an internal martial art, a style of Chinese kung fu.
How you train the form, and what you do with it is defined by this fact.
The neijia are circular and rely extensively upon spirals, curves, softness and gravity.
This must be evident in your form training and your applications.