I don't like the Wrangler because I feel that the sentry does really well on its own. Also, it gets annoying when you accidentally switch to it and then force it to be inactive for 3 seconds.
Besides, if the target is too far away, you might as well use your pistol to pick off some of their health while staying with the sentry to fix it. The Sentry isn't too effective to kill people from such a far distance, especially since the missiles take quite a while
Also, this'll teach you not to put a sentry in open areas that could easily be picked off by snipers soldiers at far distances :V