Well I'd draw a line between self-defense and the ability to fight. A focus on self-defense would say if you see someone being attacked the safest course of action is to leave the area and render no aid. As you say, one can often run away from bad situations. Thats not always possible, but it is often possible.

If on the other hand you are trying to protect others from harm you are no longer engaged in self-defense. Even if you are not physically attacking someone else but putting yourself between them and the person they are attack, that is not strictly self-defense. Most street fights turn into wrestling and longsword is often very wrestling focused. Having some knowledge of standup wrestling grappling as many HEMA schools teach gives you an advantage over most of population that have no knowledge of wrestling. HEMA is very focused on a different context so it is probably not the best way to learn such skills, but it isn't nothing either.