How about a total-return competition among these digital platforms for a same client profile (e.g. 50, 20% draw-down tolerant, S$100k cash), maybe organised by Seedly?

Total return over how many years? you will need years of empirical evidence from these robo-advisors to come to a somewhat satisying & meaningful comparision. Most of these robo-adviosrs are still in the infancy. Not to mentioned that we are still currently embroiled with the covid-19 situation, everything is distorted.

Best for now is just to compare with the common benchmark such as the S&P500

Possibly impossible. Investor situation too diverse.