It looks like malthrin's bot I may have won only because it defected on the last 2 turns. There were enough defect-on-the-last-turn bots for defecting on the last two to be a smart approach, and of the defect-on-the-last-two bots malthrin's was the closest to tit-for-tat.

In the longer evolutionary run, the winning strategy (O) was the one that defected on the last 3 turns. It stuck around until the rest of the population consisted of only defect-on-the-last-two bots (I and C4), and then it took over.

I'd like to see you re-run this competition, adding in a few variants of tit-for-tat which always defect on the last n turns (for n=2,3,4) to see whether I and O are benefiting from their other rules or just from their end-of-game defections.