No. There are many angles to consider here, and this is the conclusion some people come to when they don't appreciate that. One of DL's biggest priorities was trying to extend George Hill's contract. He just spent a 1st round pick on this guy, which you don't really want to do if you're going to lose him after one year. So If DL had burned that cap space on yet another mid level asset, he loses the ability to extend Hill. Obviously that didn't work out, but it would have been dumb not to leave that option open.
There are also other reasons for maintaining some cap space. It gives teams more flexibility to execute a trade. Otherwise, it can be difficult to meet salary matching requirements, or you might have to give up an asset to get a 3rd team involved that DOES have cap space. It also gives you the possibility of gaining an asset by being that 3rd team, helping someone else make a trade. Or you could gain an asset by taking someone else's bad contract. This is how the Nets were able to acquire Russell.
Anyway, this is a pretty common opinion around here, but wasting cap space on mid level assets can very well take you out of a bigger opportunity that comes later. No doubt if this cap space goes unused, the Captain Hindsights of the board will swoop in to trash DL, but that won't change the fact that there are some very good reasons for maintaining some cap space as opposed to filling it for the sake of filling it.