The headword phrase is quoted from the hero's speech at Sophocles, Ajax 439 (web address 1); the comment comes from the scholia there.
The participle used is the aorist active, masculine nominative (and vocative) singular, of the contract verb a)rke/w (I keep off, ward off), but here with the sense I make good, achieve; see generally LSJ s.v. a)rke/w II. [n her critical apparatus Adler notes that ms A transmits a)rke/shs, a form otherwise unattested.]
The phrase's irregular comparative (mei/w) is the neuter nominative and accusative plural (and masculine and feminine accusative singular) of the adjectives o)li/gos and mikro/s; see generally LSJ s.vv. [Adler notes that ms F reads mei/wn, the same comparative, but in masculine and feminine nominative singular; however, nothing else in the quotation suggests this choice, as e)/rga (see LSJ s.v. e)/rgon) is a neuter noun in the accusative plural, and xeiro/s (see LSJ s.v. xei/r) is a feminine noun in the genitive singular.]
[1] This adverb introduces scholia which are less than certain about the meaning of the word or phrase they are addressing; cf. generally alphaiota 66.