....would you choose the Defiance Deviant or ARC for a hunting rifle action....
It's just a question, not trying to be a smart arse.
First, I want to be clear that I am not an expert and I am well aware that there are many members of this forum with far more experience in these matters than I have.
Your question is actually a very good one because, in my mind, these ultra-high quality machined actions seem to be more suited for a "modern" type of rifle build, rather than a traditional blued steel and walnut hunting rifle. You might ask: “What is a modern rifle?” To me, a modern rifle utilizes the most modern, technologically-advanced parts available. Such rifles could fall into various categories ranging from Bench rest rifles, to ultra-long-range rifles, to sniper-type rifles, to rifles designed primarily for competition. Now, is there a reason such a rifle couldn’t be utilized for hunting? Probably not unless weight becomes a factor.
To answer your question, personally, I probably would not choose one of these actions for a dedicated hunting rifle, mainly due to cost considerations. If cost was no object, then sure, why not? Sure, you can spend upwards of 10K on a traditional hunting rifle: Serengeti, Rigby and certain fine doubles come to mind (not to mention a full custom), and you can also purchase certain “modern” rifles, which utilize these high-quality actions, for several thousand dollars as well. But why do that when a standard production rifle such as a new M70, Kimber or CZ will be perfectly adequate for the job? Because that is not the question posed by the OP. I think it all boils down to “want” rather than “need.”
We all know that the pin-point accuracy many of the modern rifles built around these high-quality actions are capable of is not needed for real-world hunting situations. Certainly, MOA or better accuracy is nice to have in a rifle, but in reality, 1.5 or even 2 MOA is perfectly adequate to dispatch game effectively in the field within reasonable shooting distances. But would I, personally, ‘want’ such a rifle if cost were no object, when I know I would be perfectly happy with a rifle built on a worked over 1909 Argentine, a K98, an Oberndorf, or a VZ24? My answer would be “definitely.” If you asked me why, I would simply say “because.” I don’t need a reason other than that is what I want. I guess I could say that I appreciate the modern technology, the tight tolerances, the light weight, and/or the pin-point accuracy at both close and long ranges.
My choice of the Defiance CRF or the Mausingfield is mainly due to the fact that these actions are CRF, which is my preference. I believe that these actions with the tight tolerances, quality machining, and modern metallurgy are an order of magnitude better, in terms of quality, than most commercial actions available today. Whether or not the machining is any better than a 1909 Argentine is a matter of debate, but the 416 SS and 4340 CM steel (just to name a few) that they are machined from is metallurgically superior to the carbon steel used prior to and during WWII. Another action I might consider is the LAW M704, which is also CRF and has the added benefit of being machined from CM steel.
So, in summary, I think it all boils down to what kind of rifle you have in mind (what you want) and your budget. While they are certainly not absolutely necessary for a dedicated hunting rig, a bunch of extremely high-quality parts screwed together the correct way can yield a very light-weight, highly accurate weapon that almost anyone would be proud to own.
Remember though, in reality I’d be perfectly happy with the cost savings of a quality traditional rifle based on a 1909 Argentine, a K98, an Oberndorf or a VZ24.