DBR, I believe that is about the best assessment I have seen here.
Properly machined barstock can be just as strong as an impact extrusion.
Thread engagement is dependent on the skill of the machine operator and his ability to set the depth of cut.
I had a 6061 Commercial extension tube fail when I knocked a carbine off of a bench and it fell butt first at angle onto a concrete pad.
The commercial stock latch was broken and the tube bent to an extent the rifle was no longer functional.
The cut threads held and no damage occurred to the receiver.
Both stock and tube were from one major manufacturer and I won't name them because it doesn't matter who, the matter is in what happened with what equipment and other manufacturers use the same set up, mainly in the interest of cutting costs to increase profitability.
Since they could use a higher grade of material in the construction of the rifles and at the current retail pricing of their rifles they could do so without adding downstream costs to the consumer,,, lets just say buying a factory made M16 type rifle is a caveat emptor proposal and the same is true for many if not most bolt, lever, and semi auto sporting rifles offered on the market so it does no good to name names.
At that point my rifle failed I immediately converted to Magpul CTR stocks with the secondary lock and VLTOR tubes.
Since I haven't dropped or abused a rifle since the last incident, I can't say for sure that the tube and stock will survive but my confidence level is high that they will.
I will name names here because this stuff is just plain well made and worth the money spent.
I also know for a fact what will fail when you least expect it to and do not purchase these items any longer.