Sorry for the delay ... I am pretty crippled w.r.t net access right now.
Note that this block is entered into after sufficient tasks have finished (given by speculation_quantile).
But you are right, we might aggressively mark too many tasks as slow and speculate when there is high skew.
If we modify such that the 'medianDuration' is not at 0.5 - but some configurable percentage of tasksSuccessful, will that address the concern ? (default to 0.5 for backward compat).
If yes, I am fine by it ... if possible, can you make the change @mateiz ? I can get to it by sat otherwise !

Thx