Some courses just happen to be more relevant to AR/AK use, and some are intentionally tailored to be specific to a certain platform. The AR platform is recognized as the standard for a combat carbine. It's what police are issued, it's what the military issues, and it's what's popular right now. The same could be said about AKs and their near-universal acceptance.
You have to tailor the rifle to the course. I have seen a course where someone brought a certain rifle just to be different and have fun, and the rifle was wholly inappropriate for the course. The instructor didn't care. In certain courses it's okay to do whatever you want. However, in other courses, it's important to have the right gun for the training. As someone pointed out above, the wrong weapon can hinder training for not only yourself, but for others and slow down the tempo of the training. You need to realistically evaluate the class and determine if your weapon platform is appropriate for that usage and employment. I intentionally take courses that are either AR-specific, or AR/AK/combat carbine (SCAR, ACR, etc)/modern battle rifle (AR10, SCAR-17, etc) specific.
The trick is to find an instructor and course that meets your needs and desires. The great thing about so much training being available is that you can tailor your training to your preferences. For instance, I intentionally choose training courses that do not allow people to use non-AR/AK/combat carbine/modern battle rifle weapons. The courses I take make those weapons problematic for the training. Additionally, I don't take tactical precision rifle/sniper courses that allow people to show up with deer rifles and benchrest rifles. But that's how I choose to select my training.
The same goes for the courses that I teach, and the weapons that I allow (and don't allow) in those courses. My courses are .le/.gov specific, and the only weapons allowed are those that are issued, carried, or relevant to their position. All students must declare their weapons ahead of time so they can be approved.
The best thing to do is to determine what weapon platform you want to shoot, and then search around for training that will allow those platforms. In your searching, you can locate instructors that have experience and expertise with that weapon. If you do that, then you can be sure to have the best experience. If, however, you take a weapon to training that you are not expertly and intimately familiar with, and the instructors there do not have much or any experience with that weapon system, you will not get as high quality of training as you would had you brought a more common weapon system like an AR. You need to be sure to locate a training program that can enhance skills that are specific to your weapon platform.