It's kind of funny, had Nick's Bebop/Rocksteady not turned on them they might have actually succeeded. Krang even says, "What happened? What went wrong?" like he was so sad because he thought he was going to win this time.
As I said, the plot in these eps of Shredder/Krang repowering the Technodrome and trying to conquer Earth with Rock Soldiers was basically the main plot of the entire original cartoon and what they were trying to do for like 10 seasons. In a way it's the perfect sendoff to the series.