I have included a link below to an article that tries to make an argument against the need for a salary cap by arguing that small market teams just do a poor job of building their teams. To make his point he makes this statement about the Reds:

The Reds have let their best players leave despite them receiving little raises in pay by their new teams.
For the life of me, I cant think of one good player, let alone their "best" players, that the Reds have recently let go into free agency and then be signed cheaply with another team. I can only guess that Dunn is who he is referring to but the Reds traded him, got value for him and probably didnt want to re-sign him regardless of the price. If anything it is just the opposite. They have re-signed Harang, Arroyo and Phillips to rather large contracts in recent years.

And as far as re-signing elsewhere for little raises with other teams, how often does a player turn down a contract with their former team thinking that the grass is greener elsewhere and then they find out it is not? The Reds are hardly alone in this regard.

Can you think of any of the Reds "best" players that they have recently let go because of salary concerns?

You don't need a salary cap, teams need to make good decisions