Personally I've always been a little concerned about the multitude of arcs in comics. Two-parters are okay, but there are a lot of comics that do 4/5/6-parters back to back throughout a series' run. The stories may be enjoyable, but it's kind of fatiguing. I can even understand the modern tendency to do this kind of thing; it helps unify the trade paperbacks. But collecting the issues month by month, I only get two, maybe three stories a year out of some titles. Sustaining interest in a single story over the course of six months gets tiring after a while.
Team-based books like JSA are a little different. They deal with major threats and a lot of characters. But Booster Gold's trending four-parters lately, with only one really nice one-shot in between.
The best example of what I mean is the "City of Crime" twelve-parter, which spanned thirteen months in Detective Comics. The story was deeply psychological and actually rather frightening, but it took FOREVER. It wasn't helped by the fact that it took a two-issue break while the "War Crimes" crossover ran. I'm sure it's a much better read in trade paperback, but by Part 12 of the initial run I was completely exhausted and hungry for something different. And quite frankly, I think the story could have been pulled off just as effectively in 8 issues.
One-parters are harder to write, yes, but check out Dini's run on Detective. Almost every issue he wrote was a one-shot, and they were great. Johns' only one-part issue on JSA (#26) was a fantastic send-off. I love the occasional one-parter because it breaks the trend and usually offers a more personal focus/off-beat story idea. I wish more modern comics would feature them.
Batman sometimes needs to use narration to help explain the mental work he performs and offer backstory/psychological grounding for a situation. It all depends on "does the text support the story, or does it repeat information already present in the art," and in most cases these days I think it's safe to say the text supports the comic.