We have to remember, these older players like Leonard are not the same guys who dominated when they made pro-bowls. The Colts reduced Leonard's playing time before they cut him because he has not been the same since his injury. Yes, he was a great player once, but he is not that guy anymore. In the meantime, Clark is having a pretty good season and he is still developing.
There is a reason these guys are all available late in the season when every team has had injuries. I would be shocked if any of these player made an impact on the Cowboys.