The last comment there speaks to me. The writer suggests that they should have had a planned story arc -including the ending- before they even began scripting the series.
JMS has proven the "story arc" paradigm works beautifully. The only "bump in the road" for the five-year arc of Babylon 5 was not JMS' fault, but the brilliant recovery of the delayed "fifth year" demonstrates that a well-developed story arc can survive even such a disruption.
As for the "Lost" series, the ones who're truly lost are the script writers...