I've done some cleanup, adding a mention of L as the series' main antagonist to the lead. I can't agree that the episode count is insignificant, given that what we're dealing with is how prominent the characters are to the story! More than that, I can't agree that L is absent from the second arc. Yes, he's dead, he's not physically present, but the characters refer to him constantly. His influence pervades the arc, as is shown by numerous quotes and so on. It's like saying Jesus has no relevance to Paul's epistles because he was dead at the time.