This is an interesting thread, I just joined it.
Clearly Richards and Koro are very different wingers, with very different skillsets.
I did not watch all the Melbourne games this year, so I cannot give a detailed opinion of how Koro performed. A lot of it is based on highlight reels, and if you critique a player based on highlights, you are a fool.
What I can say in the single game we played the Storm, we exploited Koro's wing several times and bombed the bejesus out of him, to good effect. It reinforced the opinion I had from when Koro played with us, that he is a bit of a defensive liability. Ink showed the stats, some 100% extra missed tackles than someone like Richards, who himself already missed a fair few tackles and was at times defending outside battlers like Brooks, Milone and Hoeter.
In that same game Koro scored two great wingers' tries over Nofo, but I personally feel he came out 1-2 tries in the negative based on the mistakes he made.
Clearly Koro can score a long-distance or power try as much as any winger in the comp. This should have raised his try tally even higher - if Richards managed to "stroll" across for 17 tries, did Koro only score solo efforts? Are Melbourne unable to give their wingers gift tries?
Pat Richards has aging legs, he's left us now, this argument should be really quite dead after 2015 formally concludes.
Good luck to Koro in the finals.