If it was a matter of running out of time, they probably wouldn't have given three episodes to Ash versus Paul. I don't think that's it.
Well, Ash and Paul had a rivalry that was leading up to this so they couldn't really rush the battle. And if you how long the Sinnoh League is and how rushed it seems, it becomes evident that it was a matter of time and they seemed bend on timing the premiere of Best Wishes with BW's release.
You got that right! The Legend of Korra is returning on October 3rd! Mark your calendars!