I don’t see how something can be called a martial art, as in a war art, as in something intended for the battlefield, if it doesn’t include weapons. By this I don’t just mean that there are weapons kata or separate weapons training but that the weapon is integral to the art whether or not the practitioner happens to be armed.
So Aikido is a martial art because all the techniques can be done empty hand, with a dagger, with a sword or with a staff. The distinction between armed and unarmed is meaningless from a technical standpoint, the technique doesn’t change just because you have a weapon or just because you don’t other than the other guy is going to come off considerably worse if you’re armed. In fact study with a weapon is vital to Aikido; if you don’t study with a weapon all your angles will be off.
The trouble with so many “martial” arts these days is that they are really combat sports; they evolved after the need for martial arts as defined above had passed and really they’re for fitness, or spiritual development or entertainment or purely for sporting competition. None of these arts would be viable on a battlefield. Aikido is a bit of an oddball in that it’s a modern art but it never really moved far away from Daito Ryu, Kashima Shinto Ryu and the other parent arts; it kept its emphasis on being able to use a weapon.
So then this question of multiple attackers arises and the combat sports say that it is impossible to handle multiple attackers which is born from the fact that the combat sports never attempted to address this issue. They’ve never contemplated a situation that they won’t find in competition. The martial arts, on the other hand, treated multiple attackers as the norm. In a situation where there are thousands of people on a battlefield there are going to be times when a practitioner finds themselves engaging multiple opponents, if only briefly.
This shows itself up in the technical differences between martial arts and combat sports. Martial arts are built on movement, the practitioner is constantly in motion. If you compare the tai sabaki of Aikido with say, BJJ, you notice that BJJ is a rather static art. An Aikidoka can do techniques on the move enabling them to stay evasive while also dealing with attackers. Combat sports, being static, can’t do that and being stationary their attackers are always overwhelmed. Three man attack or four man attack are normal parts of Aikido training; we do them all of the time and I’ve seen it happen on many occasions where practitioners of other arts attempt it, stand there statically as they’ve been taught to do and are promptly dogpiled.
Rather, though, than say that their art is focused on sparring up to the point of full contact sparring and no consideration is given to multiple attackers or weapons they simply declare that dealing with such things is impossible. Instead they reclassify sparring as being “real fighting” because it is full contact.