Actually, if you look at all the times he has used Thaumaturgy, he isn't using it /in/ combat. He uses it before combat gets started. For example, the illusions he puts together in the FBI building during Changes takes place before the vampires are attacking. The big earth stompah spell in South America happens before combat is engaged. Etc.
If you have a few minutes, you can pull all sorts of things together. Powerful veils, summoned allies, landmines, and so on. But you need prep time. If you got to pull off stuff with a vampire right in your face, that's Evocation. Otherwise, why have two separate powers?