The only reason to stick with Fields is to try to develop him for the future. He's had moments but overall, he is not good. The 4 wins are defensive wins. Probably would have won those 4 with Kyle Allen or Kenny Pickett.
They want to see the offense run properly. Wilson can do that. He's not perfect but he reads defenses much better than Fields.
I think it's a good move to use Rus at least for a few weeks. We need to see this offense properly run before making any impulsive trades. It could help Fields too. Let him see Rus go through progression and not look for the big play each time and see how it makes the offense run better.
Everything is connected in Smith's offense. Start completing more on time passes and it will make it easier to run.
The other factor is that there's no unbeatable team in the NFL now. With the way the defense is playing, if they get above the line QB play, as crazy as it sounds, this Steeler team does have a shot this year to make a run in the playoffs. Look at what happened with Flacco and the Browns last year. Flacco is not great but he's solid. He makes the right reads and gets the ball out on time.