I was also in the position of having one Furnace to get either Han to g9 or Luke to g9, but not both.
I ended up going with Han and wasn't disappointed. I did eventually make it all the way through to get my CLS with my Luke still g8/5
...I think you're right that the Luke event is a decent barometer for getting through CLS tier3.
And, if you did it, I might be able to get through the bonus tier of the Luke Flash event myself (still haven't done it).
...
So, since you got those 3 Omegas, have you now already Omega'd Luke's Dispel? It sounds like you probably did based on the reduced number of purple mats you listed, but I'm not sure.
Of all the places left that you could put those Mk3 mats, I think Luke's basic would be most likely to make a difference, but it's hard to tell. You've got the taunt, you've got the dispel, I would think going for damage at this point is the thing (at least with ability mats).