Commercial photography is a completely different profession. It involves many techniques and creative abilities that are very difficult to master. A commercial photographer who is good, may shoot weddings as well as most good dedicated wedding photographers can. They often can apply creative "tricks" that a dedicated wedding photographer may never have acquired. Commercial photographers often have a more extensive arsenal of high quality equipment because of the broad scope of client requirements.
So to say one is better than the other, is simply a ridiculous claim.
The main point is.. if your photographer has a good working knowledge involving his / her equipment, has an eye for the composition and is creative, he / she should do very well. There are both commercial and dedicated photographers who lack the eye, the experience or the ability, and will simply not do justice to either situation. Then there are those that just prefer one over the other and then some that can do both very well.