...there just HAS to be more relative movement with a unipivot arm than one with bearings.A broadly construed assumption that lacks clarity of formulation and overreaches in its conclusion.
First, did you ask yourself what constitutes a "bearing"? Perhaps not, because this statement implies that unipivots have no bearings. That is untrue. A unipivot consists of a "cup" and a "needle", one sitting on top of the other. These perform every function of a bearing:
1. they allow movement between two components that are in contact with each other (the armwand and arm mount);
2. they limit the direction and range of that movement;
3. they minimize friction (dependent on materials and design); and
4. they minimize "chatter" (an undesirable type of movement that causes the bearing surfaces to lose and regain contact. In short, a unipivot has bearings.
Second, you posit that unipivots allow "more relative movement" than tonearms with (other types of) bearings. Umm... what kind of movement? Relative to what?
With regard to chatter, unipivot advocates argue that a unipivot allows LESS of this relative movement than captured bearing designs. The argument is based on the fact that in a unipivot, the entire weight of the armwand is supported on a single point. In captured bearing designs, the weight of the armwand is supported by (at least) two points. Increased mass-loading of the bearing interface increases the amount of energy required to induce chatter. All else being equal (which it never is) the unipivot is a clear winner in this respect.
OTOH, a unipivot (in its pure form) is free to rotate about the tonearm's longitudinal axis, which results in changes in azimuth at the stylus/groove interface. In this respect, captured bearings may allow less relative movement. Perhaps this is what you were thinking of?
Of course, unipivot designers have adopted various measures to control/limit/prevent this undesirable movement. The success of these measures varies from absolute (eg, the secondary bearing of the Basis Vector, which arguably makes it no longer a true unipivot) to virtually non-existent, with many iterations in between employing means that range from mechanical to inertial to magnetic.
As an aside, unipivot advocates would argue that the design provides less total friction between the bearing surfaces. This of course varies with the design and materials.
FWIW, I've heard world class performance from both captured bearing and unipivot designs (far exceeding anything made by Linn, BTW). As with most high end audio gear, the devil is in the details of materials, design and construction.
Hope this was helpful.