Very interesting. But...Matthew 11:30 χρηστὸς (is easy)
Luke 5:39 χρηστός (good)
Luke 6:35 χρηστός (kind)
Romans 2:4 χρηστότητος (kindness) & χρηστὸν (kindness)
Romans 3:12 χρηστότητα (good)
Romans 11:22 χρηστότητα (the kindness) & χρηστότης (kindness) & χρηστότητι (kindness)
Romans 16:18 χρηστολογίας (smooth talk) - and that's a negative connotation
1 Corinthians 13:4 χρηστεύεται (is kind)
1 Corinthians 15:33 χρηστὰ (good)
2 Corinthians 6:3 χρηστότητι (kindness)
Galatians 5:22 χρηστότης (kindness)
Ephesians 2:7 χρηστότητι (kindness)
Ephesians 4:32 χρηστοί (kind)
Colossians 3:12 χρηστότητα (kindness)
2 Timothy 2:21 εὔχρηστον (useful)
2 Timothy 4:11 εὔχρηστος (useful)
Titus 3:4 χρηστότης (kindness)
Philemon 1:10 ἄχρηστον (useless) & εὔχρηστον (useful)
1 Peter 2:3 χρηστὸς (is good)
If we keep in mind the "unchangeability" and "fixedness" of the texts that we have, which are full of inconsistencies, grammatical errors and hilariously fake and false "prophecies" sometimes even assigned to the wrong prophet, there are only two possibilities in this matter:
1. The texts that show an abundance of this word were written when this word was considered a hot topic, and
2. The texts that show a relative absence of this word were written when this word was "just a word"
This does not hold. Again, see my proposed development.It isn't until Paul after the gospels that the new words get repurposed: χρηστός suddenly gets sexy, and so does καινός. And so the letters are relatively full of these words, and the gospels aren't - and once again it is blatantly evident that Paul is late, and somehow it just doesn't get through to some idiots' thick skulls
What you are seeing in the use of this word in the Pauline letters are the modifications that occur with the creation of the collection that includes Canonical Luke. Clearly when that collection was created, the Pauline letters were heavily revised, introducing the Pastorals, rearranging the letters, and introducing many interpolations. All of Paul is not late, just the anti-Marcionite revisions.