There are potentially very high stresses on the single ripper tooth of a subsoiler. If you're scooting along with a 70 HP tractor and a single tooth subsoiler and hit a large rock or tree root then something has to give. Many of the subsoilers shown have no shear pin protection and just like the few boxblade ripper shanks I have had to straighten, that SS shank will be the weak link.
I have snapped a ripper shank on my previous machine, a 45 HP bulldozer, and it was a big dog. I had to dig up the broken tooth and a nice butt weld made it good as new.
A real chisel plow takes lots of HP since each tooth is down deep doin gmajor work. Your 70 HP tractor could maybe pull one though. Perhaps take a look at some old used farm equipment. Subsoiler, chisel plow, ripper, all seem to be pretty much the same. I have used my boxblade teeth to "chisel plow" down about 5" pretty well.