I don't think its unrealistic at all. Teams move on from mistakes all the time. With the Reds head of baseball operations stepping down, it's the perfect opportunity.
Otherwise, I guess they should trade Winker, but he's young, under control and fits their budget and they'll never get value needed for him. In Castellanos case, they get value by simply moving the contract and using the money to replace him. In Winker's case, they will need somebody back who fits better, still replaces his bat and doesn't bust the budget. That probably means going after prospects and I think Winker is too one dimensional to command top prospects. Dealing him seems like a step backwards.
They could certainly deal Senzel, but it doesn't address the problem. It still leaves them with 5 guys for 3 positions who will compromise the team's ability to take the next step by putting them all on the field.
They could deal Suarez, but he's the one guy who might be the kind of producer who could match the main guys other teams have. Trading him would mean going back into a rebuild.
Moose is overpaid which makes dealing him difficult, and I'd rather keep him anyway. He's actually won before and is a good defender when he's not out of position and this team needs more guys who know how to win.
Votto is untradeable.
To me, trading Castellanos, and freeing those resources, is the only one who would allow them to move forward. Any of the others are either untradeable or probably wouldn't net a return or free enough resources to replace their production while providing a better fit.
So if dealing Castellanos is off the table, I kind of agree that they are stuck. The only hope is that they could package other salaries with somebody like Winker to allow them to sign what they need. Maybe something like Winker, Miley and Barnhart for prospects would allow a move, but that will require signing another starter, which would be good anyway, but now we're getting into the "sweeping changes" that most people are against and I'm not sure there is enough money to address other holes created by dealing more contracts. This team has a lot of arbitration raises to deal with. Resources are going to be tight. That's why Castellanos is the best guy to deal. If they can't dothat, they probably are stuck. If so, I wouldn't expect to be winning anything anytime soon.