I think maybe its either changed or didn't have access to the trees. The description of Retribution and patch notes does not mentioned aura so implies its not part of the aura chain. Also spell focus was not taken which gives +2 to a spell dc which is too good to miss out on if you go t5 Tainted Scholar. So 2 points spent on spell focus and 1 left over which I think 1 point in the 1st core or Soul Eater for 5 USP is best option.
But, just checked points spent on t4 ES is 9 when it should have been 7. So a further 2 points is also available.
Something I will check when I hit 20, unless anyone has checked if Retribution works without aura and if it procs empyrean. If so, then I may put 4 points in the line for 1d6 light damage to get the up to extra 10 spell crit chance from it. Another thing would be interesting to know if the alignment damage (uses light spell power) from Utterdark Blast procs it also which would mean little reason to get Retribution.