One could say the G4 writers might have been more used to writing episodically. They have less experience with things like character development and story arcs.
I might not agree with you much on Starlight, but here's a thought to tickle our brains. I think Starlight in Season 5 was not brought up enough only anticipation for the Season Finale. She could have appeared in multiple episodes building up tension over time in significant ways not just a cameo in an episode.
I think G5 writers might now be more willing to follow a continuity and treat it like a full on story since they are looking at the show in hindsight instead of in the middle of it.