It's in the movie. Riker asks why they're not sent to the battle and Picard says it's not the ship, it's its captain. Comet-counting isn't banishment. It's what Starfleet does. New ship does only that til it can prove it can also fulfill their secondary mission. When the Borg show, the ship is kept away because of its captain. They're the flagship crew. On the new flagship. It's only the Borg Starfleet is antsy trusting Picard on, with good reason given his actions in the movie. Maybe because it was special enough to get the upgrades whereas no-one cares about an 80-year old Miranda serving cargo and transport duty (like the Excelsiors were) before desperate times made it cannon-fodder. A more important mission for the moment. Yes. Whatever their esthetic shortcomings, they're the latest and greatest out the dock. They're going to be used in crucial positions while more are being built. They were probably holding together whole systems (or sectors!) by themselves so that all the older ships therein could join the Galaxy fleets during the invasion of Cardassian space. Or maybe Admiral Ross was on one.