Good armor will protect the user against a lot throws. The protection is provide not only from impact resistance of the armor, but also the additional mass, and size the armor gives to the body. Multiple that by two if both are in armor.
By way of example, and speaking somewhat generally:
The arm cannon (forearm, elbow & upper arm as one piece) will prevent the elbow from being hyper-extended. That's assuming that you can grab the arm with your hands. In most cases the armor will add enough circumference to make it difficult to do so. In terms of attacking an arm for a submission or throw, the armor makes this very difficult.
Good chest & back armor will keep your spine straight. It adds enough girth to the torso that wrapping an arm around that torso will be difficult. Since both people are wearing armor, that makes it even more difficult to do so.
Judo and modern grappling in any form is geared toward unarmored fighting. Fighting in armor is very, very different. Judo will help you understand leverage, but it's really hard to directly apply many techniques to someone in armor. If you don't understand leverage, yes, Judo will be beneficial, otherwise, not so much.
Most modernly practiced eastern arts aren't as focused on armored combat any more. Even those that have an armored combat curriculum, won't translate well to the sport. European armor is very different. The weapons are very different. The sport has rules (no thrusting) that need to be observed. Using an eastern martial art as a base might not be the best option.
Swordplay is not universal, in the most surprising of ways. It also is surprisingly similar. A Katana is not a longsword ( General examples: the curve, and lack of quillons causes the katana issues when defending the thrust. It's curve makes some arm and hand attacks possible, that aren't from the longsword). Nor is it a saber ( general examples: sabers tend to be more heavily curved, giving them more cutting options than the katana. The katana would be better at the thrust). It's not even remotely close to a falchion.
As a black belt in Kenjutsu, and studying Western Martial arts for the last 5+ years. Find yourself a local SCA, or WMA group. They'll be much closer to what you'll experience doing BotN and other armored sport combat.