It isn't fundamentally easier to control an arm than a tentacle; That is human intuition based on the fact that we have arms. Limiting the number of degrees of freedom is something done at the level of experimental design for the production of chemical libraries. DNA is already a programmable medium for nanorobotics, and skilled genetic engineers can do atomically precise peptide biosynthesis for the sake of NMR spectroscopy. It does not seem as though you are informed of bionanotechnology in the present.
Octopodes do not beg to differ, they tergiversate to genuflect.
The thing to recognize is that tentacles predate arms, legs, or fins by millennia. Jellyfish tentacles have fewer kinds of parts than any arm, hence they constitute simpler machines.
In the paper you cite, humans are describing cephalopods with a model based on their own anatomy; it is not the other way around, as you claim.
