Frankly, I find not interesting the icosathlon.
The decathlon, even if rewards the muscular power, maintains a certain balance in speed, strength, agility, coordination and resistence/endurance, with three events in the jumping area, three in the throwing, and four in the running races (of which two sprints, one resistance to the speed and another cardio-respiratory endurance).
The icosathlon, on the contrary, penalizes both the jumps that the throws, possessing only four events each, while the running races will have twelve.
In addition, the muscular and nervous fatigue that accumulates during the days of icosathlon competition, prevents, in the last events of every day, that the athlete can deliver its real potential.
In conclusion, the icosathlete is more resistant but less complete than the decathlete.