This one is easy. Yes, your martial arts instruction should cover joints extensively. This includes things like the use of joints, the training of joints, striking with joints, striking at joints, the protection of joints, and health maintenance of joints. But this is not something I would call theory; there is very little abstraction when talking about joints.
General meridian theory is not really helpful for learning to fight and train; it is not going to tell you that your shoulders are not flexible enough to hit hard, you haven't developed sufficient sensitivity to pressure to avoid overcommitting, or your feet need more coordination.
Your system should have a roadmap for body and skill development, and it is important that you understand this roadmap. Your sifu should be a guide in this respect, helping you to understand where your body's feedback puts you on the roadmap, and what training elements are necessary to continue your journey. Understanding your body cannot come solely from book knowledge; you have to put in the training hours. If your system roadmap is written in the language of qi, you should develop a clear bodily feeling/understanding of what is meant by this language for your system for particular exercises.
Continuing with the roadmap analogy, a good martial arts system will:
- Lead you to a useful destination. This can include things like ability to fight and understanding of how to improve/maintain health.
- Have enough clearly-marked signposts along the way that you can tell what direction you are heading. Understanding of meridian theory may be of side interest when feeling that when your foot gets warm your leg also feels full, but your understanding of whether your foot has achieved sufficient coordination and relaxation will not be impacted.
- Have teachers and other students to assist your navigation.
If you have been training for years and do not understand what you need to practice to progress, there is a problem.
Traditional Chinese Medicine
This is not something that will help you fight directly. TCM theory will do things like help you determine diet, treat injuries, and address physical problems, but it will not help directly with striking, throwing, and other fighting skills.
I would actually expect skills to be more transferable going the other way; many of the physical practices associated with martial practice will help a medical practitioner understand a patient's physical state and how they can be treated. Exercise (mental and physical) is a primary mechanism of health preservation and improvement in TCM.
A good teacher-student relationship includes the open asking of questions. A teacher may not be able to answer all questions or may tell you that you are not ready for the subject (the inner-door issue), but there should not be an issue with asking. Do not expect your teacher to be a mind reader; if you do not express interest, then your teacher has no way of knowing about your interest.