considered righteous and justified are not the same term, but you interchange them as desired in your argument
Justification is at the most basic level all about being found (legally) righteous or just by God (cf. dikaiosuné from dikaióthénai "to be made/declared righteous"), thus Matthew 12:37 uses it as an antonym of katadikasthésé "condemned" and Paul associates it with judgment (Romans 3:4, 5:9, 1 Corinthians 4:4) and the remission of sins (Romans 6:7, 1 Corinthians 6:9-11; cf. Acts 13:38-39, Galatians 2:17), and the citation from Genesis 15:6 concerning Abraham (used by both Paul and the author of James) refers to the justified patriarch as being elogisthe ... eis dikaiosunén "reckoned into righteousness" (Romans 4:2-3; cf. 4:5 concerning the Christian believer). This continues the sense of justification from pre-Christian Judaism in which "righteousness" was construed as fidelity to the Torah (Deuteronomy 6:25, Luke 1:6; compare Malachi 3:18, Matthew 5:20), which provided for atonement and expiation of guilt (cf. Leviticus 1:4, 4:20, 7:7, 16:1-34, 17:11). Justification can of course be differently defined, nuanced, and construed in Christian theology so justification is not simply "interchangeable" with a notion of reckoning one righteous, but since Genesis 15:6 is alluded to in Romans 4:2-3 and James 2:23, it is quite appropriate to make reference to the basic sense of the term.