Was Rusty to the rescue necessary? 

I’ve seen two adaptions of rusty to the rescue that not only give rusty a staring role but stay true to stepney’s real life history.

Even though I much prefer the Railway Series take on Stepney, this is still a great episode.

At least, Rusty, an innocent and reasonable little diesel, becomes a major player with his own spotlight story of his own.

Bluebells of England on its own would not have made a good TV episode, but I don't think RTTR was the right solution to that problem. Thomas & Stepney combined Bluebells of England and Stepney's Special, and could (and should) have been more faithful in doing so. The biggest problem with S4's handling of Stepney was the fictionalization of a real engine's backstory, which completely undermines the entire point of the book's existence. Wilbert, a passionate advocate for railway preservation, wanted to promote the Bluebell Railway, and watching it on TV, you wouldn't necessarily know that the Bluebell Railway is a real railway or that Stepney is a real engine.

The dialogue in the episode doesn’t make any sense. So no.