The comparative expresses contrast or comparison. Thus, δεξίτερος is right in contrast to its opposite, ἀριστερός
εὖ τε καὶ χεῖρον
a. When the positive precedes, μᾶλλον alone may stand for the comparative; as in ἐκεῖνοί τε ἄξιοι ἐπαίνου καὶ ἔτι μᾶλλον (i.e. ἀξιώτεροι)
b. The persons or things with which comparison is made may include all others of the same class: ἡμῶν ὁ γεραίτερος
Herbert Weir Smyth [n.d.], A Greek Grammar for Colleges; Machine readable text [info] [word count] [Smyth].