I think the challenge of this debate is that everyone is going to have a different concept of what arc is, since arc material is what could disqualify an episode from stand-alone status.
To me, something like death-of-personality as a punishment is not arc. It's a piece of the Babylon 5 universe, and it can be used more than once, but it doesn't progress, it doesn't grow, it just *is*.
Same with organic tech, aspects of telepathy, and the alien healing device. They *serve* the stories, but they are not *the* story.
I keep trying to think how I would define "arc", but it's tough to do and very subjective. Think of Babylon 5 as a tapestry. Telepathy, death of personality, organic tech, the alien healing device, etc. are the way in which the threads are weaved to make the tapestry. They're the foundation; they define the bounds and the extent of what can come about in the Babylon 5 universe. They're the "stuff".
The Shadow War, the Narn/Centauri rivalries, the Earth & Minbari civil wars, the Sheridan/Delenn/Sinclair trinity, the fall of Londo, the ascension of G'Kar, the rough lives of Ivanova & Garibaldi, the latter fifth season "goodbye" episodes, and yes, even Byron and his ratty band of psycho-hippies

are the dye in the threads of the tapestry. They define the color and the pattern of the tapestry. They're the reason you want or don't want to buy the "stuff". The color and pattern are the arc.
More material, less color & pattern... That's a stand-alone episode.
Eh, sucky analogy.

My apologies.

And I'll admit, the alien healing device is still borderline. For a cheap prop with huge potential to be a one-hit wonder, it does have pivotal importance in the lives/death of three main characters.
