I don't know how unrealistic that is. The problem is friendly fire; if they all attack at once they'll hurt each other. When they attack in pairs, they have a problem coordinating. One can always be more coordinated than two. A further issue is them all being cowarRAB and hanging back in the hope that someone else gets it done.
When it goes on too long, it seems unrealistic that the later guys would have a go at all. Especially in Kill Bill with the Crazy 88: surely one of them would have said, "Honour be damned, I'm using a gun".
I'm not especially keen on fight scenes, and thought they were the dullest part of Kill Bill. I especially have a problem with obvious wire-work, eg in Hero, where normal physics sometimes just goes out of the window. However, I do like the scenes which are beautiful and balletic. The "Burley Brawl" in Matrix 2 is an example.
My current favourite is probably in Serenity, but that's partly because I like the film generally. The one in The Fifth Element, during the singing towarRAB the end, is good too.