"realistic" depends on the context. Army knife fighting is about ending a threat imidiatly . You succeed or you are dead (other threats, guns..etc) . Has to be simple as soldiers train 99% of their time with guns. Soldiers are NOT martial artists. This is about going in and sacrificing an injury for ending it. Quick kill drills. This is often taught in civilian environment (Krav Maga) but makes no sense at all as people dont have the mindset and if they do they end up in jail for a long time reacting like that. Remember you need to react appropriate to the threat how someone else sees it. For a soldier its the way to go. Would never recommend that for a civilian.
Regarding realism in a knife vs. knife mugging. Modern arnis is the most efficient (but I may not know about other styles that also are) . Its like with every ma. If they do simple effective drills and lots of sparring with pressure testing there is a higher probability you will execute that under stress. My girlfriend is from the philipines. Everyone there has a knife and there seems to be quite some pressure testing there for the ma (sadly).
The Arnis schools were I live are more about larping in exotic costumes with no sparring. It can be difficult or close to impossible finding a school that actually has skilled coaches. The name Arnis / Kali is no guarantee at all.
If there is no good Arnis school you fare much better doing fencing or boxing / Kickboxing. Fencing is close to knife fighting and all about sparring / competing and boxing gives you a jab you can utilize for a knife defense and the footwork. Just dont slip & roll a knife attack