A Y link is a form of radius arm links. Any axle articulation requires deflection of the bushings, but most systems will allow enough deflection to make it work. It tends to wear out the bushings faster because of this. If the arms are long enough deflection doesn't seem to limit usable articulation.
A true 4 link doesn't have any binding, so articulation is dependant on shock length mostly, and possibly bushing deflection if bushings are used rather than joints. The XJ's front is a type of 4 link, the arms aren't trianglated enough to provide lateral axle control so a track bar is used. The track bar will cause some binding in the links and limit articulation at some point, depending on arm length and angles and type of joints. A true triangulated 4 link doesn't need a track bar to locate the axle laterally and there is no binding when articulated.
A 3 link must use a track bar to locate the axle laterally but will have no binding when articulated. Since the XJ's engine is so far forward, it's difficult to build a triangulated 4 link, so many of us build a 3 link.