The alternative
Ball bearings
They are indeed used in very popular tonearms at all times. Todays high tech manufacturing allows to create bearings with incredibly low tolerances. The bearings used in the Schick arm have 0 (zero) positive tolerance and 7µm negative tolerance. From a perfect ball the negative tolerance means 'dents' with 7µ depth. Since there are many balls holding the construction the probability of really having 7µ tolerance is extremly low. This gives an extreme stable connection beetween the moving parts.
top quaility ball bearings
But low tolerance gives the bearing another desired property: Quietness. Obviously noise of the tonearm bearings would cause movement and resonances in the arm, that would cause a loss of information again. The low tolerance surface is achived by polishing, which makes the surface of the modern ball bearing very smooth and silent if turned. It is possible o buy an identical looking bearing for a fraction of the cost. Turn them and put them to the ear. You can hear already metallic scratch noises, nothing you would like to have in the music signal.
Turn a vintage SME arm hrizontally and you know what I mean.
The low tolerance and smooth surface has a thrid important feature, low friction and low stick effect. The mechanical momentum necessary to start moving is very low. Thus the cartridge can again tracks better. The super smooth surface also makes the friction very low. We are talking of values where regular grease would be like like fixing glue. For lubrication a special very light oil is used.
A word to the life expectancy of the bearings. They are made to withstand really high revs. That will never occur in their tonearm live , but ensures their quality for decades.
Material choice
Apart from the crucial moving part of tonearms, much talk is around about resonances. Metal is usually a good resonator, which is bad. But metal is strong and rigid. In a mechanical assembly the resonances of the metal can be kept very low. If two 'ringing' pieces of metal are brought together and joined mechanically, they do not produce any sound anymore. So the use of a headshell is a very good treatment for the arm resonances. The mechanical interface between the arm tube and the plug controls the resonances very good. The same applies at the pivot axis and the counterweight. All three elements are joined together in order to control the resonances.
Arm Geometry
Another point worth looking at is the geometry of arms. Pick up arms can be designed to have a minimum of tracking distortion by bending them and use them with an overhang of the needle. For this calculation two points have to be chosen where the circular movement meets the tangential line of the record cutting machine.
earlier choice of zero points
Often, especially with older designs, these point are too wide from each other, resulting in positive tracking distortion all over the record. The points were put at the outer radius of the label and the outside of the record. The amount of distortion is viewable by the amount of the surface between the green and pink line.
Have a look at your records. Where is the last piece of music? The needle approaches its ideal in the outer groove wher no more music is recorded.
better choice of zero points
A better approach is to put the points closer together. This way the overall distortion is much smaller. The curve is much closer to the ideal tangential line.