Nope. The Spurs would have paid Hill, without a doubt. They loved Kawhi more, and sending Hill was the only way to get him.
This time, they wanted both Carroll and Morris. They knew that they needed the entire MLE to be able to sign Morris (they thought). So they couldn't use any of their MLE to sign Carroll. They sent Bertans to the Wiz for a trade exception, which they used to sign Carroll, specifically so that they would have the whole MLE left for Morris. That's the long and short of it.
If they had kept Bertans, they would have still had the entire MLE open for Morris, so long as they didn't sign Carroll. They shipped Bertans for Carroll, who they don't even play. Colossal up.
You could say that they were worried about what they would have to pay to keep Bertans after this year. But the alternative was letting him walk for nothing, right? Well they shipped him out and got...nothing. Because a player that never gets on the floor is nothing.