Actually, I wonder if he just wasn't as invested in it. He only wrote one or two episodes this season, and at the time, he would have been working on All-Star Superman premiering and Justice League: Doom, along with all the hype for the Milestone characters being inducted into DC before the reboot. Or possibly with it coming to the end, just being more lax. I hate saying it, but it seems to be a trend with shows he was in charge of: the last season of Static Shock was widely accepted as terrible, he Vilgax arc of Alien Force, and now Ultimate Alien.