That is true enough. However it should be pointed out that the many, most? the majority? of gunsmiths "assemble" rifles as well. Of course there are gunsmiths that chamber barrels themselves. Personally (as long as you start with a quality action) I'd rather have the barrel chamber by say a Bartlein, CarbonSix etc where they are likely using much better milling machines than the typical gunsmith, particularly if you provide them with a new reamer. There are of course exceptional gunsmiths, but the cost and wait time goes up accordingly.
Perhaps I am lucky but the rifles I have "assembled" with quality parts, BAT, Lone Peak, Trigger Tech, Hawkins, CarbonSix, Benchmark, Manners, MPA, XLR shoot and function as well as my TS Custom (which is great). I get the hesitancy of people to tackle a rifle project on their own. The components aren't inexpensive, fear of the unknown etc. For example I have a friend that takes scopes to a gunsmith 2 hours away for mounting. The thought of doing it himself scares him to death, much less "assembling" a rifle. But if you have the time, a little mechanical competency, the right tools and a sense of adventure it is a lot of fun.
The feeling of satisfaction gained by a successful hunt with a rifle for which you selected and acquired the components, "assembled", mounted the scope, developed and loaded the ammo (also "assembly") is immense.