I think the real problem is that what you tend to see in taiji is people doing the form. That is all they are taught, and they are taught the form starting on day one. In that case, knowing the applications from the form is useless because they lack the larger context of having a working foundation and don’t even know how to throw an effective punch.
Forms are worthless without understanding the foundation. Forms should not be taught until later, when they have value with context. Why is it that people want to jump straight into the forms, and teachers are apparently willing to do so? What other martial art does this? A karate school or a Tae Kwon do school or a kung fu school that develops students into capable fighters or people with functional self defense skills spend time developing the basics, the punches and kicks and blocks and stepping and whatever other techniques are in the arsenal, so that a student understands how to use them. How to use a punch in a more generalized sense, how to harness good biomechanics according to the training methods of the particular style.
If taiji schools approached training in this way, they would look much like other kung fu or karate schools. Students should be learning to punch by throwing hundreds of punches in a training session and getting instruction on how to do that effectively. Instead, they come to class and do the form two or three times, and then go home. Maybe the Sifu “shows” them a couple of applications, and then training is finished. People think they are learning taiji for fighting, but they are fooling themselves.
When someone can throw an effective punch and has an understanding of how to use the punch in a confrontation, then they can begin learning what the form contains. Then they have the foundational context to make sense of what is in the forms, and learn further applications from them.
If someone jumps straight to the form and that is all they train, you can spend eternity showing them applications from the form, and they will never benefit from it. Because it never gets drilled in a way to really develop the skill, it becomes theoretical knowledge that they can never apply.
Unfortunately I believe there is a general trend in other kung fu schools to jump straight to the forms and short-change the fundamentals and the foundation. That is a recipe for learning a form as a hollow dance routine, and not as a meaningful training tool.
People gotta put in the hard work and gotta spend their time on the basics. Taiji is no exception to this. In my opinion, that is what is missing in most modern taiji schools.
So getting back to what I quoted above, I believe two years of taiji could be enough to have some solid application, if those two years are spent learning how to throw a solid punch and gaining an understanding of how to do so in a confrontation. It isn’t learning the form and people would think it doesn’t look like taiji. But taiji folks need to develop those basics just like anyone training a different system. For some reason people have decided that taiji is different, it only requires doing the form a couple of times and the movement of the form will magically transform them into a capable combatant. It won’t. Only hard work will. What is kung fu? It is skill gained through hard work. Most taiji people have no kung fu.