The intended Lorelai/Christopher relationship arc, imo, was set up to be portraying Chris as an adolescent girl's romantic fantasy. Lorelai fell in love with when she was a teen, and part of her is still in love with him.
Her maturation, then, would be coming to realize that Chris -- charming, irresponsibile, well-meaning but ultimately shallow -- isn't who she wants as a life partner. He's still an overgrown teenager, and she needs an adult.
That arc doesn't quite work as the series played out, though. Lorelai would never had married the Chris who failed to show at important events in Rory's life -- graduations, birthdays, etc. Chris wasn't in Thailand, he was a few hours away, in Boston.
The reason Chris wasn't at those events wasn't because ASP intended him to seen as a villain, but because of actor availability issues. These issues ruined the whole Lorelai/Chris arc.